The correct way to do this is to create a new user with lusrmgr.msc and then use the User Profiles dialog "Copy To..." feature to copy the old profile to the new profile.
Also, don't use spaces and don't use any special characters, only "[0-9a-z_-]". Diacritic characters in polish are handled wrong by so many apps, which is a shame, because "user" in polish is "użytkownik".
Did this once for macOS & never got VLC to work properly again since it kept caching the older username in some location & it was now unable to access some property...
