@codeDude There is a service which gives you standard XMPP addresses for Matrix rooms and users: https://archon.im/arianet/matrix-homeserver/services/
It's sometimes very slow to respond though. I couldn't join a channel via @gajim last time because there is a 10s timeout for the server to respond (but it did respond eventually).
Some Matrix rooms are also connected to IRC. In this case it's best to join the IRC channel via Biboumi: https://joinjabber.org/tutorials/gateways/irc/