> They already require that you use Sign in with Apple, I would think that it working fully is also a requirement?

They require apps offer a service which meets their privacy requirements if they use any 3rd party or social login service.[1] And apps could block private.icloud.com for email and not Sign in with Apple.

[1] https://9to5mac.com/2024/01/27/sign-in-with-apple-rules-app-...