Yes, propably Facebook login. Meaning if it is in on self hosted one, users should connect alternative way to login. Or they have to use password restoring.
It looks like time of SSO via social media is over. It doesn’t mean any bigger, because Google and Microsoft covers majority of users. Apple would be bice addon, but because of theirs greediness it is an option only on corporate level. And there is, of course, still the traditionally way spiced up with tools of devices.
Instagram embeds has always been as big headache as Xwitter login, and if/when it disappears we don’t loose nothing good.