We moved off IRC to Slack ages ago. Then they decided Slack was too expensive so we were forced to Teams which is bundled with the inescapable O365 license. We now use IRC again (UnrealIRCd) which runs on a debian VM on someone's workstation in the office.
irssi is surprisingly decent, and would even makes you think IRC the protocol was designed around irssi (and TUI), although the protocol is actually much older
Clients are all irssi on WSL2 or Macs.