Sign in with Apple
Sign in with Apple allows you to sign in to third-party apps and websites using the Apple ID you already have. If the app or website supports Sign in with Apple, you see a Sign in with Apple button when you try to sign in or set up a new account.
See the Apple Support article What is Sign in with Apple?
To learn how Hide My Email works with Sign in with Apple, see the Apple Support article What is Hide My Email?