If a developer says "The blocker for me is IntelliJ supporting Java 21",
clearly there's an IDE dependency. Powerful enough for a developer
not to adopt a new framework.
But writing any language is much more productive with a good IDE. For me, the added value in using Java 21 now rather than in a few months is not enough to outweigh giving up the use of an IDE.
Time to add a format check to pre-merge CI.
Being a bit entitled regarding support of preview features.
If said developer is savy enough to use a preview SDK, they should be able to cope with the downsides of lacking all the nice support.