On iOS, Sign in with Apple will provide an e-mail address if the user is logging in for the first time. On all subsequent logins, the e-mail address will be missing. However, this can be reset by removing the app from your Apple ID. If you then try to login again, the e-mail dialog will popup again, and the app will receive this e-mail.
On visionOS, however, the latter does not happen. Even if I have removed the app from my Apple ID, the e-mail dialog won't show up again. The only way to resolve this is to reset the visionOS simulator (haven't tried it on a real device).
