IRC is dead to many people, however it is a communication method/medium that has outlived a lot of other services that have come and gone over the years.
IRC doesn't seem to have much new uptake these days as younger folk or newer projects seem to prefer chat networks like Discord. However there is still a reasonable user base on various IRC networks particularly among open source projects.
While you can build, run and host your IRC server, most people use one of the existing IRC networks that run the infrastructure.
There are multiple IRC networks still running, Netsplit.de have a Top 100 list based on the networks that participate in their comparison.
As there is no client/server syncing model in IRC, to maintain a connection to the network and consistent conversations, you would normally leave a client running and connected.
I run a self-hosted web client at home called The Lounge, this client maintains a connection to the IRC networks and channels that I am interested in.
I access the web client over Tailscale using a browser on my computer or mobile device, assuming my home Internet is up, the web client is reachable to me wherever I am.
Below are a couple of screenshots of
The Lounge on a mobile web browser.