The meeting itself
Jitsi Meet
Screen sharing, integrated chat and HD Opus audio are stated, and the selective-forwarding architecture comes with published load numbers — 1056 streams at over 550 Mbps for about 20% CPU — plus a Last-N mode that trims distribution to the most recent speakers and distributed tracing across the backend. What I could not find is a published participant cap per meeting, breakout rooms, or a lobby; on meet.jit.si moderation is described as "soft, and for everyone" because all users are moderators, with strong authentication available only on instances customers run themselves.
Nextcloud Talk
The only capacity numbers on file are '6-10 participants, up to 20 if all participants have a good network connection and do not use video' for a private setup, and a vague 'thousands' for enterprise — nothing tied to a plan. Breakout rooms exist and the constrained-connection honesty is welcome, but the webinar lobby needs the High Performance Backend, and screen sharing, mute-all, waiting rooms and any bandwidth-adaptation claim are simply absent from the evidence.