The numbers here https://netsplit.de/networks/top100.php are much lower than what I remember from twenty years ago, and the Internet Archive seems to support this: https://web.archive.org/web/20060902133725/http://irc.netspl...

I don't think IRC is one of those technologies whose usage count in absolute terms is at an all-time high today. It wasn't exactly mainstream in the early 2000s, but it still had lots of users.