As per the new account deletion requirements that became effective on june 30th (https://developer.apple.com/news/?id=12m75xbj) it is now required that account deletion within an app calls apple's API to revoke user tokens.
Deleting the firebase user does not do this. Is it possible then to extract the apple auth ID/token from firebase? Otherwise I can't think of any other way to abide by the guideline.
I'm just going to update this immediately as I've found the answer to my own question - no, and the firebase team is working on a proper long term solution, but that won't be out until Q42022 or Q12023.