This "Mac Catalyst With Apple Sign In" Demo is very simple & easy to understand about How to develop Catalyst app and sign in with Apple. This demo includes Login screen, sign in with apple and home screen.
This swiftUI Demo is very simple & easy to understand. This swiftUI demo includes On-boarding screens, login screen, forgot password screen, sign up screen, home & logout.
If you are an aspiring iOS app developer, make yourself aware of the Apple backed Swift language and its applications and here is the guide for the same.