Teams users cannot sign in if using personal account

This is for a new Windows 11 installation I did yesterday and may be of some help for that message of not being able to log into Teams with a personal email, no matter what I tried.  Since Skype was not installed, I downloaded a Skype installation package from a third party which still had it, and when Skype was started, it gave me the message that Skype was discontinued, and there was a button to use Teams instead which I pressed.  Immediately my entire Skype account was automatically transferred into MS Teams without even having to log in to Skype. The problem most likely arises from my having just a simple username rather than an email or number (mobile) for Skype because I started using Skype way back when it came out from Germany, even before eBay and then Microsoft owned it.