Camera only allowed for a few users

Is there an option to prohibit users from turning on their camera? So that only moderators can have the camera on?
I would like to allow only 5 users to use the camera in meetings with e.g. 100 participants, the others should only be able to listen and watch.

It would be perfect if users can make a request for camera activation and the moderator can approve it.

Yes, we call that advanced moderation. Check the “…” button at the bottom of the participant’s pane.

I can use it to disable the camera and microphone for a user, but they can enable it again themselves. The module av_moderation is also enabled in the prosody.
Do I have to allow anything extra for this?

In the following topic someone has apparently got the option enabled:

Untick the options which allow the users to unmute themselves in the menu.