Impressed by your attentiveness. I’m sure prosody is a fantastic product, I don’t mean to drag it through the mud.
What I should expound on is that in the Jitsi server configuration that out of the box they don’t have good documentation for getting room size, participants, total number of rooms etc. I did find the Jitsi community forums where the Jitsi devs tell community members how to enable some prosody plugins. There was an issue for my vanilla configuration where I needed to update Lua and download 5 other lua rocks. Then the mod-muc-size plug-in needs to be modified and the nginx configuration needs to be updated as well. This is my rough memory from a month ago.
So it would be nice if Jitsi had a more out of the box solution for this integration, and I understand prosody is just a piece in the whole production.
https://github.com/jitsi