@martin Thank you, however I believe all others should be deleted as well (leaving some random/dummy value as per my previous reply)
I believe for that reason those values already exist under default
and still no user can use them, unless Admin decides to allow their usage - deleting from that list from admin panel.
And in my opinion for self-hosted setup its better to give a freedom to admin to decide.
Please consider this scenario: I want to add account with name moderator, with existing setup I have to ssh to my server change site settings file (deleting the value in mandatory_values) and restart the container to be able to do it (and after rebuild this change is being reset).
But, if all values (well, except one) from mandatory_values are deleted (but NOT from default), as Admin I can simply delete “moderator” value in admin panel (under reserved usernames), quickly rename some existing user’s username to moderator and again add the word moderator - to prevent future usage.
So, with my suggested approach still all those usernames are disallowed by default, however admin can easly delete/add them whenever needed without being have to make changes in site settings files.