I'd imagine most web savvy people these days have several email addresses and lots of us will use disposable emails or tricks like adding '+something' to our emails when we sign up.

I've recently run into this problem on a couple of sites [I'm thinking Trustpilot and Mastodon but could be wrong], whereby my password manager had saved my login name and password but, when I returned to the site, it wanted me to login with my email address and password. [inconsistent naming of form fields twixt registration screen and login screen, no doubt].

I couldn't remember which of my half dozen or so email addresses or "+"-added variations of them I'd used, or if I'd used a disposable email like Mailinator to sign up. So I clicked on the "forgot login" link --which then asked enter my account email address, in order to be sent a password reset link!