IRC is only text chat, Discord does a ton of other things on top.
Personally I’ve been on the internet for the last… 27 years or so? I’ve used ICQ, Teamspeak, Skype, IRC, Mumble, Discord, Teams, … (Probably forgot a few).
I never really liked IRC, yes, it’s private servers which is nice, yes you can be relatively anonymous, but the channels were always a mess. Either too many people spamming so you can’t follow a single conversation, or for most channels you had 40 people idling and never responding, so it felt like a ghost town.
Just in my personal experience Discord works a lot better and is far more convenient. But yeah, not much privacy there obviously (though everything you said in IRC was often saved away by a bot, so either way whatever you said was out there).