I don't have much to add other than I'm getting the same issue on the same package/file . I just upgraded from X Code 14 to 15.6 beta. Seems to be on the FIRFirestoreSettings file. I also cannot find anyone talking about on the Firebase Git Hub.

I found a work around. I'm just using X code 15.6 and it works.

Somehow it's now broken again. I switched from my main branch back to branch one and now xcode 15.5 is broken now with the same error. I managed to get it to build once without any issue.