We regularly run it with 40-50 users, and it's fine... as long as you limit the number of displayed video streams to 12-15 or fewer. This tends to happen organically with people muting video, or otherwise you can configure Jitsi to limit it to show video for the last 12 people who spoke.

Otherwise you risk overloading people on devices which can't render >12 simultaneous video streams without melting. You can push the limit higher if you know everyone is on a fast machine however.

One thing worth noting is that if a one or more user connects via Firefox then quality degrades for everyone - but fixes for this look to be in flight over at https://github.com/jitsi/jitsi-meet/issues/4758