No, you're clearly correct. But Apple pushing this does give it a sense of legitimacy and blocking signups from this service might just cause less signups than actually forcing people to use their real address.
If Apple makes this extremely user friendly and quick to use than blocking it will cause a loss of signups.
‘Error: We love Apple and anonymity but we require a real email address to prevent fraud and to properly secure your account. Please enter your real email address.’
It would work roughly the same way. Integrating an OAuth provider like this requires registering an application with revokable ClientIDs, so Apple can technically pull them just as easily as they can pull Apps.
(It remains to be seen if they'll put in the legwork to actually police these things, though)
> ‘Error: We love Apple and anonymity but we require a real email address to prevent fraud and to properly secure your account. Please enter your real email address.’
GDPR would probably want to know specifically why you need someone's real email address.
If Apple makes this extremely user friendly and quick to use than blocking it will cause a loss of signups.