The documentation here says that the sign up with Apple button is available on web: https://developer.apple.com/design/human-interface-guidelines/sign-in-with-apple/overview/buttons/
However in the Apple JS documentation, it shows only 2 buttons (sign in and continue) as being available:
https://developer.apple.com/documentation/signinwithapplejs/displaying_sign_in_with_apple_buttons
Can we expect the "Sign Up" button to be available in Apple JS soon?