White Noise, which is based on the MLS protocol, uses Nostr to transmit the data. It's entirely decentralised. It has good support for large groups

This podcast episode is a nice intro: https://fountain.fm/episode/gzfxBKiY94NTCUKySPQ2

I'm very impressed. But it's still relatively new. The MLS protocol is not new, it seems to be well regarded. But the rolling out into the real world is still in the early stages