Highlights include Sliding Sync (instant login/launch/sync), Native OIDC (industry-standard authentication), Native Group VoIP (end-to-end encrypted large-scale voice & video conferencing) and Faster Joins (lazy-loading room state when your server joins a room).
@pezhore XMPP and IRC (to my knowledge, which very well may be outdated) are quite similar - you join a room from a client, you get a nickname, maybe a few lines of history, you chat, you close your client or lose connectivity, you don’t know anymore what’s happening there. You want to join from another client, that’s a separate session, with a different presence and name on the channel. Your clients don’t share history etc. [2/n]
That’s not true in the case of XMPP: upon reconnecting, any modern client will request from the server enough messages to recreate the missing history (of course it’s up to you/the client to put a limit to that if you want).
I think even IRC(v3) is taking that route.