Greetings,
As the subject says, creating a local, unattached account has been turned off as part of the single-user login finalization process taking place over the next two months. This is to prevent any further usernames from being created that are going to clash with global accounts when the great renaming process happens[1]. Going forward, /all/ new user accounts on the public farm will be global in nature.
I am sorry if this inconveniences anyone, feel free to contact me with questions.
1. https://phabricator.wikimedia.org/T70069