Oh wow thanks, I was trying in "Other C Flags" and "Other Swift Flags". Just tried again using User-Defined Settings and it now works. It needs to be added to any target which imports AppIntents.

@appleSince80 Does this workaround works for you? I've already tried it and it doesn't help. Also tried increasing deployment target, didn't helped.

I've got the same problem. For now I'll have to build with Xcode 15.2. Filled a report too that you can reference: FB13812719. Hope this will get fixed!