I have this issue today. My application rejected because they couldn't sign in with apple on iPad with iOS 14.1. All simulators have 14.3 and I have the spinning icon signing in with my Apple ID. All simulators with iOS 13.2 work just fine for apple sign in and my real device with 14.2 works as well. I am using Xcode Version 12.3 (12C33).

I had this issue yesterday. My application rejected because they couldn't sign in with apple on iPad with iOS 14.1. All simulators have 14.3 on my Mac, and I have the spinning icon signing in with my Apple ID on all simulators with iOS 14.*. All simulators with iOS 13.2 work just fine for apple sign in with the application. My real device with 14.2 works as well as all testers using iOS 14.1 and 14.2 on their devices including iPad devices. I am using Xcode Version 12.3 (12C33).

I am having this same issue.