Iām looking to extend the macro-kanban.
Can someone give me a hint about the development workflow to optain the same result as seen in the repository?
Is the development done inside of xwiki and then exported in some way or is it done outside and then a POM is generated from source files?
Yes. In the ... page menu you have an Export ā XAR (if you are admin). The XAR file is a zip which contains those XML files.
See Development Practices (Community.DevelopmentPractices) - XWiki
Thank you. When I do that I only get one xml file with all the content inside. In the github there are multiple files. Should I export every file separately?
The page menu export only exports that page, yes, but you rarely need to modify all the pages of an extension when you implement/fix something.
Alternatively, you go to Administer Wiki ā Content ā Export where you can select several pages to export.