I'm experiencing this problem with iOS 15.4. I have to switch to an iOS 13 simulator to make it work, but then the rest of my app doesn't behave as expected, so I have to switch back to iOS 15.4 simulator and hard code a user ID. This is not a sustainable workflow. I'm very surprised that a native capability is not working in iOS simulator. Can someone from apple please let us know when this will be fixed? this seems to be an issue for over a year now without any response. OK Ive decided to ditch sign in with apple. I will not offer this to my customers because it is too difficult to get working.