Teams for Mac retains deleted personal Microsoft account in account picker after alias change

Since the stale account does not appear in a brand-new macOS user profile, I’d agree this is probably local identity cache in the original profile rather than the Microsoft account itself.

I’d quit Teams and all Office apps, then rename rather than delete the Teams and Office identity containers so you have a rollback. Also check Keychain for old entries tied to Teams, OneAuth, ADAL, MSAL, login.microsoftonline.com, and the old alias. After that, reopen Teams and sign in fresh.

If the stale account survives that, it may be worth opening a Microsoft support case as a Teams/OneAuth cache bug and include your “new macOS profile is clean” test, because that’s a very useful clue.