I was integrating Apple Sign In and followed the below official documentation except the part where it was stated we needed to dive into XCode for some configuration.
I deployed into Apple App Connect, and added the build into TestFlight.
Apple Sign In works without any issues and WITHOUT requiring the XCode configuration stated in the documentation.
Hope this helps other future FF users integrating Apple Sign In, you don't need to delve into Android Studio to configure XCode in Runner. You do however need to configure and add all the App IDs and Service IDs that are stated in most tutorials.
https://docs.flutterflow.io/integrations/authentication/firebase/apple/