Excel plugin not working anymore

Since last week, the excel plugin is not working anymore on my xwiki platform
OS = Ubuntu 22.04.3 LTS
xwiki-common 14.10.19
xwiki-mysql-common 14.10.19
xwiki-tomcat9-common 14.10.19
xwiki-tomcat9-mysql 14.10.19
Excel Plugin 1.1

I noticed there was an upgrade of openjdk on Nov 30:
2023-11-30 06:47:47 upgrade openjdk-8-jre-headless:amd64 8u382-ga-1~22.04.1 8u392-ga-1~22.04
2023-11-30 06:47:50 upgrade openjdk-11-jre:amd64 11.0.20.1+1-0ubuntu1~22.04 11.0.21+9-0ubuntu1~22.04
2023-11-30 06:47:50 upgrade openjdk-11-jre-headless:amd64 11.0.20.1+1-0ubuntu1~22.04 11.0.21+9-0ubuntu1~22.04

The testpage

{{velocity}}
$xwiki.calc
{{/velocity}}

returns the error
Failed to execute the [velocity] macro. Cause: [jxl.write.WritableCell]. Click on this message for details.

org.xwiki.rendering.macro.MacroExecutionException: Failed to evaluate Velocity Macro for content [$xwiki.calc]
at org.xwiki.rendering.internal.macro.velocity.VelocityMacro.evaluateString(VelocityMacro.java:135)
at org.xwiki.rendering.internal.macro.velocity.VelocityMacro.evaluateString(VelocityMacro.java:51)
at org.xwiki.rendering.macro.script.AbstractScriptMacro.evaluateBlock(AbstractScriptMacro.java:279)
at org.xwiki.rendering.macro.script.AbstractScriptMacro.execute(AbstractScriptMacro.java:182)
at org.xwiki.rendering.macro.script.AbstractScriptMacro.execute(AbstractScriptMacro.java:58)
at org.xwiki.rendering.internal.transformation.macro.MacroTransformation.transform(MacroTransformation.java:309)
at org.xwiki.rendering.internal.transformation.DefaultRenderingContext.transformInContext(DefaultRenderingContext.java:183)
at org.xwiki.rendering.internal.transformation.DefaultTransformationManager.performTransformations(DefaultTransformationManager.java:88)
at org.xwiki.display.internal.DocumentContentAsyncExecutor.executeInCurrentExecutionContext(DocumentContentAsyncExecutor.java:395)
at org.xwiki.display.internal.DocumentContentAsyncExecutor.execute(DocumentContentAsyncExecutor.java:268)
at org.xwiki.display.internal.DocumentContentAsyncRenderer.execute(DocumentContentAsyncRenderer.java:112)
at org.xwiki.rendering.async.internal.block.AbstractBlockAsyncRenderer.render(AbstractBlockAsyncRenderer.java:157)
at org.xwiki.rendering.async.internal.block.AbstractBlockAsyncRenderer.render(AbstractBlockAsyncRenderer.java:54)
at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.syncRender(DefaultAsyncRendererExecutor.java:290)
at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.render(DefaultAsyncRendererExecutor.java:267)
at org.xwiki.rendering.async.internal.block.DefaultBlockAsyncRendererExecutor.execute(DefaultBlockAsyncRendererExecutor.java:125)
at org.xwiki.display.internal.DocumentContentDisplayer.display(DocumentContentDisplayer.java:67)
at org.xwiki.display.internal.DocumentContentDisplayer.display(DocumentContentDisplayer.java:43)
at org.xwiki.display.internal.DefaultDocumentDisplayer.display(DefaultDocumentDisplayer.java:96)
at org.xwiki.display.internal.DefaultDocumentDisplayer.display(DefaultDocumentDisplayer.java:39)
at org.xwiki.sheet.internal.SheetDocumentDisplayer.display(SheetDocumentDisplayer.java:123)
at org.xwiki.sheet.internal.SheetDocumentDisplayer.display(SheetDocumentDisplayer.java:52)
at org.xwiki.display.internal.ConfiguredDocumentDisplayer.display(ConfiguredDocumentDisplayer.java:68)
at org.xwiki.display.internal.ConfiguredDocumentDisplayer.display(ConfiguredDocumentDisplayer.java:42)
at com.xpn.xwiki.doc.XWikiDocument.display(XWikiDocument.java:1355)
at com.xpn.xwiki.doc.XWikiDocument.getRenderedContent(XWikiDocument.java:1492)
at com.xpn.xwiki.doc.XWikiDocument.displayDocument(XWikiDocument.java:1441)
at com.xpn.xwiki.doc.XWikiDocument.displayDocument(XWikiDocument.java:1410)
at com.xpn.xwiki.api.Document.displayDocument(Document.java:786)
at jdk.internal.reflect.GeneratedMethodAccessor1963.invoke(Unknown Source)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.doInvoke(UberspectImpl.java:571)
at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:554)
at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:221)
at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:368)
at org.apache.velocity.runtime.parser.node.ASTReference.value(ASTReference.java:704)
at org.apache.velocity.runtime.parser.node.ASTExpression.value(ASTExpression.java:75)
at org.apache.velocity.runtime.parser.node.ASTSetDirective.render(ASTSetDirective.java:242)
at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:147)
at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:439)
at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:190)
at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:147)
at org.xwiki.velocity.internal.directive.TryCatchDirective.render(TryCatchDirective.java:86)
at org.apache.velocity.runtime.parser.node.ASTDirective.render(ASTDirective.java:304)
at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:439)
at org.apache.velocity.Template.merge(Template.java:358)
at org.apache.velocity.Template.merge(Template.java:262)
at org.xwiki.velocity.internal.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:280)
at com.xpn.xwiki.render.DefaultVelocityManager.evaluate(DefaultVelocityManager.java:328)
at com.xpn.xwiki.internal.template.VelocityTemplateEvaluator.evaluateContent(VelocityTemplateEvaluator.java:95)
at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.evaluateContent(TemplateAsyncRenderer.java:222)
at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.renderVelocity(TemplateAsyncRenderer.java:177)
at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.render(TemplateAsyncRenderer.java:138)
at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.render(TemplateAsyncRenderer.java:54)
at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.lambda$syncRender$0(DefaultAsyncRendererExecutor.java:284)
at com.xpn.xwiki.internal.security.authorization.DefaultAuthorExecutor.call(DefaultAuthorExecutor.java:98)
at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.syncRender(DefaultAsyncRendererExecutor.java:284)
at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.render(DefaultAsyncRendererExecutor.java:267)
at org.xwiki.rendering.async.internal.block.DefaultBlockAsyncRendererExecutor.render(DefaultBlockAsyncRendererExecutor.java:154)
at com.xpn.xwiki.internal.template.InternalTemplateManager.render(InternalTemplateManager.java:843)
at com.xpn.xwiki.internal.template.InternalTemplateManager.renderFromSkin(InternalTemplateManager.java:805)
at com.xpn.xwiki.internal.template.InternalTemplateManager.render(InternalTemplateManager.java:792)
at com.xpn.xwiki.internal.template.InternalTemplateManager.renderNoException(InternalTemplateManager.java:747)
at com.xpn.xwiki.internal.template.InternalTemplateManager.renderNoException(InternalTemplateManager.java:739)
at com.xpn.xwiki.internal.template.DefaultTemplateManager.renderNoException(DefaultTemplateManager.java:79)
at com.xpn.xwiki.internal.template.DefaultTemplateManager.renderNoException(DefaultTemplateManager.java:73)
at org.xwiki.template.script.TemplateScriptService.render(TemplateScriptService.java:54)
at jdk.internal.reflect.GeneratedMethodAccessor1533.invoke(Unknown Source)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.doInvoke(UberspectImpl.java:571)
at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:554)
at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:221)
at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:368)
at org.apache.velocity.runtime.parser.node.ASTReference.render(ASTReference.java:492)
at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:147)
at org.apache.velocity.runtime.directive.VelocimacroProxy.render(VelocimacroProxy.java:218)
at org.apache.velocity.runtime.directive.RuntimeMacro.render(RuntimeMacro.java:331)
at org.apache.velocity.runtime.directive.RuntimeMacro.render(RuntimeMacro.java:261)
at org.apache.velocity.runtime.parser.node.ASTDirective.render(ASTDirective.java:304)
at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:439)
at org.apache.velocity.Template.merge(Template.java:358)
at org.apache.velocity.Template.merge(Template.java:262)
at org.xwiki.velocity.internal.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:280)
at com.xpn.xwiki.render.DefaultVelocityManager.evaluate(DefaultVelocityManager.java:328)
at com.xpn.xwiki.internal.template.VelocityTemplateEvaluator.evaluateContent(VelocityTemplateEvaluator.java:95)
at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.evaluateContent(TemplateAsyncRenderer.java:222)
at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.renderVelocity(TemplateAsyncRenderer.java:177)
at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.render(TemplateAsyncRenderer.java:138)
at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.render(TemplateAsyncRenderer.java:54)
at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.lambda$syncRender$0(DefaultAsyncRendererExecutor.java:284)
at com.xpn.xwiki.internal.security.authorization.DefaultAuthorExecutor.call(DefaultAuthorExecutor.java:98)
at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.syncRender(DefaultAsyncRendererExecutor.java:284)
at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.render(DefaultAsyncRendererExecutor.java:267)
at org.xwiki.rendering.async.internal.block.DefaultBlockAsyncRendererExecutor.render(DefaultBlockAsyncRendererExecutor.java:154)
at com.xpn.xwiki.internal.template.InternalTemplateManager.render(InternalTemplateManager.java:843)
at com.xpn.xwiki.internal.template.InternalTemplateManager.renderFromSkin(InternalTemplateManager.java:805)
at com.xpn.xwiki.internal.template.InternalTemplateManager.render(InternalTemplateManager.java:792)
at com.xpn.xwiki.internal.template.InternalTemplateManager.renderNoException(InternalTemplateManager.java:747)
at com.xpn.xwiki.internal.template.InternalTemplateManager.renderNoException(InternalTemplateManager.java:739)
at com.xpn.xwiki.internal.template.DefaultTemplateManager.renderNoException(DefaultTemplateManager.java:79)
at com.xpn.xwiki.internal.template.DefaultTemplateManager.renderNoException(DefaultTemplateManager.java:73)
at org.xwiki.template.script.TemplateScriptService.render(TemplateScriptService.java:54)
at jdk.internal.reflect.GeneratedMethodAccessor1533.invoke(Unknown Source)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.doInvoke(UberspectImpl.java:571)
at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:554)
at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:221)
at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:368)
at org.apache.velocity.runtime.parser.node.ASTReference.render(ASTReference.java:492)
at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:147)
at org.apache.velocity.runtime.directive.VelocimacroProxy.render(VelocimacroProxy.java:218)
at org.apache.velocity.runtime.directive.RuntimeMacro.render(RuntimeMacro.java:331)
at org.apache.velocity.runtime.directive.RuntimeMacro.render(RuntimeMacro.java:261)
at org.apache.velocity.runtime.parser.node.ASTDirective.render(ASTDirective.java:304)
at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:147)
at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:171)
at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:147)
at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:439)
at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:190)
at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:439)
at org.apache.velocity.Template.merge(Template.java:358)
at org.apache.velocity.Template.merge(Template.java:262)
at org.xwiki.velocity.internal.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:280)
at com.xpn.xwiki.render.DefaultVelocityManager.evaluate(DefaultVelocityManager.java:328)
at com.xpn.xwiki.internal.template.VelocityTemplateEvaluator.evaluateContent(VelocityTemplateEvaluator.java:95)
at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.evaluateContent(TemplateAsyncRenderer.java:222)
at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.renderVelocity(TemplateAsyncRenderer.java:177)
at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.render(TemplateAsyncRenderer.java:138)
at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.render(TemplateAsyncRenderer.java:54)
at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.lambda$syncRender$0(DefaultAsyncRendererExecutor.java:284)
at com.xpn.xwiki.internal.security.authorization.DefaultAuthorExecutor.call(DefaultAuthorExecutor.java:98)
at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.syncRender(DefaultAsyncRendererExecutor.java:284)
at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.render(DefaultAsyncRendererExecutor.java:267)
at org.xwiki.rendering.async.internal.block.DefaultBlockAsyncRendererExecutor.render(DefaultBlockAsyncRendererExecutor.java:154)
at com.xpn.xwiki.internal.template.InternalTemplateManager.render(InternalTemplateManager.java:843)
at com.xpn.xwiki.internal.template.InternalTemplateManager.renderFromSkin(InternalTemplateManager.java:805)
at com.xpn.xwiki.internal.template.InternalTemplateManager.renderFromSkin(InternalTemplateManager.java:785)
at com.xpn.xwiki.internal.template.InternalTemplateManager.render(InternalTemplateManager.java:771)
at com.xpn.xwiki.internal.template.DefaultTemplateManager.render(DefaultTemplateManager.java:91)
at com.xpn.xwiki.internal.template.DefaultTemplateManager.render(DefaultTemplateManager.java:85)
at com.xpn.xwiki.XWiki.evaluateTemplate(XWiki.java:2563)
at com.xpn.xwiki.web.Utils.parseTemplate(Utils.java:180)
at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:651)
at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:339)
at com.xpn.xwiki.web.LegacyActionServlet.service(LegacyActionServlet.java:114)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:764)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
at com.xpn.xwiki.web.ActionFilter.doFilter(ActionFilter.java:122)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
at org.xwiki.wysiwyg.filter.ConversionFilter.doFilter(ConversionFilter.java:61)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
at org.xwiki.container.servlet.filters.internal.SetHTTPHeaderFilter.doFilter(SetHTTPHeaderFilter.java:63)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
at org.xwiki.resource.servlet.RoutingFilter.doFilter(RoutingFilter.java:132)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
at org.xwiki.container.servlet.filters.internal.SavedRequestRestorerFilter.doFilter(SavedRequestRestorerFilter.java:208)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
at org.xwiki.container.servlet.filters.internal.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:111)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:540)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:687)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:359)
at org.apache.coyote.ajp.AjpProcessor.service(AjpProcessor.java:433)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:889)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1735)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.base/java.lang.Thread.run(Thread.java:829)
Caused by: org.xwiki.velocity.XWikiVelocityException: Failed to evaluate content with namespace [xwiki:WOK -HOME.Test Page.WebHome]
at org.xwiki.velocity.internal.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:289)
at com.xpn.xwiki.render.DefaultVelocityManager.evaluate(DefaultVelocityManager.java:328)
at org.xwiki.rendering.internal.macro.velocity.VelocityMacro.evaluateString(VelocityMacro.java:127)
… 188 more
Caused by: org.apache.velocity.exception.MethodInvocationException: Invocation of method ‘get’ in class com.xpn.xwiki.api.XWiki threw exception java.lang.NoClassDefFoundError: jxl/write/WritableCell at xwiki:WOK -HOME.Test Page.WebHome[line 1, column 8]
at org.apache.velocity.runtime.parser.node.ASTIdentifier.execute(ASTIdentifier.java:260)
at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:368)
at org.apache.velocity.runtime.parser.node.ASTReference.render(ASTReference.java:492)
at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:439)
at org.apache.velocity.Template.merge(Template.java:358)
at org.apache.velocity.Template.merge(Template.java:262)
at org.xwiki.velocity.internal.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:280)
… 190 more
Caused by: java.lang.NoClassDefFoundError: jxl/write/WritableCell
at com.xpn.xwiki.plugin.excel.ExcelPlugin.getPluginApi(ExcelPlugin.java:62)
at com.xpn.xwiki.XWiki.getPluginApi(XWiki.java:6673)
at com.xpn.xwiki.api.XWiki.getPlugin(XWiki.java:2331)
at com.xpn.xwiki.api.XWiki.get(XWiki.java:2320)
at jdk.internal.reflect.GeneratedMethodAccessor1529.invoke(Unknown Source)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.apache.velocity.runtime.parser.node.GetExecutor.execute(GetExecutor.java:118)
at org.apache.velocity.util.introspection.UberspectImpl$VelGetterImpl.invoke(UberspectImpl.java:722)
at org.apache.velocity.runtime.parser.node.ASTIdentifier.execute(ASTIdentifier.java:217)
… 196 more
Caused by: java.lang.ClassNotFoundException: jxl.write.WritableCell
at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:476)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:594)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:527)
… 206 more

Excel Plugin (XWiki.org) shows: " * Download the Java Excel API and copy the jxl.jar file to the %xwikipath%/WEB-INF/lib/ directory of your xwiki installation."
I downloaded the jexcelapi_2_6_12.zip, unzipped the file, copied the jxl.jar to the WEB-INF/lib directory and restarted tomcat9.
Problem solved!
But I do not understand why this problem all of a sudden appeared. Was the jxl.jar file removed by some update?