See also the categories listed in the system dashboard: Loading...
The proposal is to remove that category from JIRA since it’s hard to maintain and doesn’t bring much value for the users. The proposal is also to not add that category in OP.
+1
AFAIK, there’s no indication about what this category means exactly. The meaning of “Supported” evolved in our community and a category “XWiki supported” does not convey enough information to be relevant anymore. The missing information becomes obvious when comparing it to the support information on an extension page: