I think Matrix is a good upcoming contender. The available clients are not really mature yet though. Element is excessively heavyweight and bloated, being Electron based. Other clients all seem to miss some essential feature or other. And there's no good archiving solution yet.

Matrix has/had a great archiver at https://github.com/matrix-org/matrix-viewer - but it fell foul of the bizarre failure mode that folks who had explicitly set their rooms to be archivable had subsequently forgotten that they had, and then went absolutely berserk when they discovered their rooms having been archived: https://matrix.org/blog/2023/07/what-happened-with-the-archi.... This was one of the reasons given for libera to turn off the libera<->matrix irc bridge.

At the time we had much bigger problems to deal with, so we shelved it and have yet to get back to it.