Hi.
Go to: Options > Users > Change permissions
Scroll down to "Show_group_members", change the setting from "Default" to "Modified" and add a mark in the "Broadcaster" column then, at the bottom of the screen, click the "Save changes" button.
Note that in sub-forums any permissions are inherited from the parent forum, so you can, for example, stop those in the "Anyone" or "Registered" groups from creating new topics or replying but allow broadcasters to do so.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.