If your application uses the Bitcoin Core RPC you should test it with v28.0, either rc2 or the final release.
E.g. the (unmaintained) rpc-bitcoin npm package accidentally broke: https://github.com/vansergen/rpc-bitcoin/pull/65
Discussion
I believe the current plan is to have a v28.1 release later that's a little bit more relaxed about weird invalid stuff. So if things break, and you can't quickly fix them, maybe wait for that release.
But don't wait passively: actually open a github issue.
