Yeah, that screen was most unwelcome today and I saw it more than once. I saw it on exactly that same session, so apparently it was wildly popular.
It's not as if we were all streaming our camera output to each other like in a Zoom or Teams meeting. It was one presentation and slides. Why was there a limit, and what was it just out of curiosity?
Are you seeing these messages for sessions or interactive labs? The screen shot is for an interactive lab, which has a 200 person limit. The labs make use of VPN and VNC to connect to systems at MacStadium, so I can see they they would have a limit.
But if this is regular sessions as well...