Eventually you might realize it’s based on an open standard https://openid.net/2019/09/30/apple-successfully-implements-... and that it’s relatively similar to other such standards, except with the option to mask your email, etc.
As an geeky end user, the only way I trust these services for login is if I can link more than one, or even more than one email from the same provider. That way I know I’ll have a backup in case I lose access to the social network or email address that I signed in with... it’s annoying when I can’t add a password or set an email just because I also want to login without a password sometimes...
It's still incomplete, their implementation deviates from the standard or use some lesser used mechanism like the form_post response_type, requiring custom code.
Implementing this was not a pleasant experience.