To my knowledge, the core of Twitch chat is just IRC[0]. They've obviously extended it a fair bit, but it's probably the largest service I can think of that leans on the protocol.
I visit a /g/ adjacent channel regularly on Rizon. I've also interacted with two software projects on Libera in the last 6 months. So yes, it is still active.
I use some IRC channels on Libera IRC, and there are some people writing to most of them often enough; I also write on IRC sometimes.