How do I know if an add on is supported in a new version of JIRA

[Nic Brough -Adaptavist-]

The marketplace entry for add-ons lists the compatibility and supported versions.

Remember that vendors are not always perfect, sometimes a version that doesn't work properly creeps into the wrong numbers. 

More importantly, it takes time to make add-ons compatible, or even just test them and change the numbers, so give them a chance.  There's far too many questions here demanding "when will add-on x be ready for version y" the day after Y is released, and that's just unfair - vendors might only have a few days before the release, if any time at all, and have other things to do that are more urgent.