No. We’re very careful about backward compatibility when changing out APIs so if it works on 9.8.1 it should work on newer versions of XWiki, but of course, since it wasn’t tested on XWiki 11 it means there can be unknown / hidden problems that you may encounter.
Note that if you like the XWiki open source project then by buying a license for a paid app you are in fact contributing to the development of XWiki. But if you bought a cloud instance then it means you are already doing this, which is great and we are thankful.
Thanks,
Marius