Windows set up with Microsoft Account uses abbreviated e-mail for user names, because UTF-8 breaks apps, including many East Asian apps. non-Western Windows us

Windows set up with Microsoft Account uses abbreviated e-mail for user names, because UTF-8 breaks apps, including many East Asian apps. non-Western Windows users always knew never to use anything outside ASCII for usernames, passwords, or any programmatically used identifiers. It's English users that haven't learned it.