i’m connected with legacy password system.
I try to create a new user (in the user management menu) , i have the popup with name, login, password, but when i click on create i receive an red unauthorized message.
I’m using last hassio version (0.81.6) but already have the same when testing with previous version.
you probably need to login with the user created when you updated to a new version of HA that does the new authentication, then you can create more users.
i found a fix here.
Basically delete the .storage folder and restart the server and when it comes back it will ask to onboard a new user and then the new user can create more user as mentioned by @lolouk44.