As an aside since you brought up Undernet: Their CService website[1] has been down for weeks now. As far as I know, that's the only way to even register with X. I'm not sure if this is being worked around, somehow, or if UnderNet is just being left to die.
I help run a irc network which was spawned out of Undernet #linux around 15 years ago, because even back then we were really unhappy with general instability and how Undernet was run. Back then, it would split or simply go down several times a day.
We were making the claim that “Undernet is dying” even back then.
A few people and #linux channel-ops legitimately asked “How hard can it be?” and surprise surprise: not very.
So here we are 15 years later, aside from some very few incidents, with almost zero downtime.
Some servers has gone, some new have arrived. Same with oppers.
But the network is still there and all the same IRC-clients and users can still reach us.
IRC is one of the best things Internet has to offer, and these days people are working furiously to avoid learning what has made it so great.
It amuses me a little that this mirrors how Undernet itself got started - in that case, by the ops of #hottub on Dalnet.
There's a certain whimsical botanical style to the way in which IRC networks tended to grow large enough to start budding off new networks, some of which were able to find sufficient purchase to grow large themselves and repeat the cycle anew.
[1] https://cservice.undernet.org/