Oh, I have never heard of mostly matter, and I think that’s a nice initiative.
As mentioned over in Feedback on Collaboration for Mission-Critical Work, Framasoft is maintaining a soft fork called Mostlymatter that removes the arbitrary user limits.
- The downloads are here: https://packages.framasoft.org/projects/mostlymatter/
- The patch’s source code is here: https://framagit.org/framasoft/framateam/mostlymatter
System76 migrated to Mostlymatter in late February for the Pop!_OS community chat, and it seems to be working well. (As explained in that other thread, we do have far fewer simultaneous users than registered users, and while I expect many servers are like that, YMMV based on your own server loads.)