It's not foolproof, but given I'm generating the password in Bitwarden anyway, it's not the end of the world if it doesn't catch it.
I too have struggled to remember which third party sign-on I used (or if I used a native sign in), so now I avoid them every time, too.
They're literally only convenient if I want to have an account that I'm happy to 'throw away' or, to accidentally create duplicate accounts for the service.
For anything where I'm actually paying, they're a nightmare. Oh, did I sign into this with one of my google accounts? Was I crazy enough to use facebook? Or which of my emails did I use?
I suppose that's a huge assumption, but that's how I would do it if I was developing against them. That said, it doesn't help w/ the "Hide my Email" or the default icloud.com email addresses people don't realize they're using.
But if you have a Password Manager, then it is literally a single signon solution in and of itself, without the sacrifice of privacy.
Probably, and this shouldn't be a thing. Except maybe for banks, but even then, it's debatable. Here's a handy list of cases when I want to be logged out:
1. I click the log out button.
Which I don't ever do either, because it's my personal device.
Account creation sucks, but I prefer it to letting an ID provider know about it. Although I would trust real third party ones like auth0 more than Facebook or Apple, even if they have a more focused business model.