The meeting itself
Jitsi Meet
The selective-forwarding bridge comes with published load tests — 1056 streams at over 550 Mbps for about 20% CPU on a rentable server — plus a Last-N mode that documents behaviour under load, and screen sharing and integrated chat are on the product page. But the pages say every participant is a moderator on meet.jit.si and the controls are "soft, and for everyone", so host control is shared rather than reserved. We found no public information on breakout rooms, waiting rooms, layout control, or behaviour on mobile networks.
Nextcloud Talk
Breakout rooms, a lobby and a stated scale range are real, but the evidence never evidences screen sharing at all, and the only constrained-connection behaviour on record is 'up to 20 if all participants have a good network connection and do not use video'. No adaptive bitrate, no diagnostics, no per-plan capacity — I cannot credit a call the evidence won't show me.