Yes, but compared to "modern" apps IRC is very rudimentary and you would not get messages if you "close the app". You always have to run some secondary infrastructure like a bouncer to get offline messages or see what happened while you were away.
I know that's not the fault of the protocol itself, but that's always one of the biggest hurdle for IRC adoption when everyone is used to just open apps and see the full history at all times.
Oh thanks for the note about ergo.chat, need to have a play with this!
Ergo looks really cool, will have to take a look at that. Thanks for sharing.
The protocol needs ugly extensions to have a variety of devices plug into the same user account. For me back in the day this was an ssh session running the IRC client in a screen, and it was no worse than whatever else was available.
IRC client in screen/tmux is still my gold standard. I like having the same full-fat client on my phone instead of a lesser one. I have scripts and aliases set up in irssi and I can still use those from my phone.
Mobile devices are different devices with different constraints. The main blockers are intermittent connectivity and the need to save battery life.