How to disable topic capability within desired forum
Let’s say there is a place in the forum where we don’t want users to be creating new topics. They should be allowed to post in existing threads. This can be easily implemented over administrator control panel at permissions section.
Firstly, login to administrator control panel and click on “PERMISSIONS” tab in the top menu.
After that click on “Group forum permissions” under “FORUM BASED PERMISSIONS” section.
It will open a list with available user groups like administrators, moderators, registered users, etc. From this list select “Registered users” and click “Submit” button.
In the next window select the forum name in which users won’t be allowed to create new topics and click “Submit” button.
Then click on “Advanced Permissions” which will populate the list of advanced permissions for registered users. From this list find “Can start new topics” and select checkbox for “No”.
Finally, click “Apply permissions” in order to save the changes. From now registered users won’t be able to create new topics in the selected forum.