Don't know when exactly, the available options are Google and Apple.
What a brain fart! You can't link Apple, because, guess what, the email is already linked to... Google! What an utter nonsense!
By the way, it's a design flaw to associate "social" logins with their emails! I've recently been in situations where a person was rehired into a different role with the same email address but a different Google Workspace ID, and their previous permissions were suddenly reinstated with a vendor. Auth0 does this correctly, though - email and user ID are separate identities. This sometimes creates headaches, but it's a top-notch security practice! I guess the only exceptions would be if your email is gmail.com, icloud.com, or me.com, with respect to Google and Apple "social" logins.