Question about usersBrowser Info Environment
Users are either manually added to the Forum Users group in the Dashboard by admin or they can apply for forum access from their user page, but the admin will still have to approve them. The addon doesn't do this automatically.
To add bulk users to the addon, there's a button Add All Users from Group in Dashboard > Forum > Users. But the users have to be added to the group by admin first in any case. After they're added, you can bulk approve them.
Please have a look if there's an addon which will add registered users to a group.
I have extended the user group functionality: now you can add users to the Forum either from a selected group or all site users.