This does not seem to be blocking, but just incase:
In a Debian Bookworm server with XWiki-Xjetty, I got these error messages when checking for updates in the extension section of the administration panel.
Here is a sample of the messages:
Checking for updates...
Could not validate integrity of download from https://nexus.xwiki.org/nexus/content/groups/public/com/nimbusds/content-type/maven-metadata.xml
Starting job of type [upgradeplan] with identifier [extension/plan//wiki:xwiki]
Checksum validation failed, no checksums available
……
…………
Resolving extension [org.xwiki.rendering:xwiki-rendering-macro-figure/16.5.0] on namespace [Home]
Could not find extension [org.xwiki.rendering:xwiki-rendering-macro-figure/16.5.0]
Checksum validation failed, no checksums available
Checksum validation failed, no checksums available
and some warnings.
I can provide the full message if it can help in any way.