[uda]

1. This isn't a clear cut, though some services don't allow using both Oauth 2.0 and email / username login, most do. So if the service provider allows both, create a simple user + link your account.

2. Developers should always allow restoring passwords for SSO only users, it is ridiculous for it to even be an issue.

3. As a user, refrain fro using free email accounts to identify on a platform, as others already said, buy a domain not an expensive one, and stick to it, remember to renew, and setup your email address with a reliable service, there are good providers for $1 a month.

Update: line separation...