Merges in 3.9.16. Merge with a merge commit when tests pass. DO NOT SQUASH OR REBASE.
@Fedik is anything required to port from #27561 - I'm really not sure right now - I feel like it's not an issue because nested fields are entirely encapsulated - but not 100%
The stuff in #27562 is already ported in here. Just the sub form field itself change that I mentioned and if not porting it is the correct fix that’s perfect :)
@wilsonge yes it need to fix for J4 also, but I already made a pull for that #27562
you can skip "porting", and check that pull instead ;)