The initial version of your comment essentially stated that rebuttals are not welcome (still kinda does, since the stated goal is to avoid rehashing old discussions).
But just to give you some kind of rebuttal (or mention some unmentioned points by you): IRC has native clients for many more operating systems than any alternatives (many don't even have any native clients at all!). IRC will still work when everything is very broken (DNS on fire, AWS having a moment, ..) and I think a fair few still use it for that reliability aspect. UX is very much in the eye of the beholder. Chatops is very much a thing in IRC as well as adding commands to it (just with ! instead of /).
Yes, which is why I reworded it. The score continued to decline.
Honestly, everything I've posted here is a list of facts. I'm more than willing to entertain being wrong on one or more of them, but as far as I can tell those facts are not actually in question.
Regarding your edit, that could be seen as a benefit that IRC has, but right there with that would have to be "native clients" on the list of things that most people don't care about. The hatred of non-native packaged web apps is mostly a techie thing that doesn't exist outside of forums like HN. In a world where electron didn't exist, there would be a world with less platform support, not a world with more native apps.
I would actually still disagree a lot here, since a lot of the points you list under "Things every other modern messaging solution is better at:" for example is either things IRC has had forever (more fine-grained permissions and authentication; file transfers; abuse control and prevention; extensibility of all things.. nothing beats IRC here), that are really in the eye of the beholder (UX) or are things that not even most modern solutions have (threading; actual file sharing (good luck with large files); screen sharing) - some may have some subset of the features, but I don't think all of them have all of them.
Fair point that the non-native apps are something people don't actively think or care about (even if it's the cause their battery is flat all the time). It's just personally I want to avoid applications that use a significant fraction of my ram and cpu just to display 10 lines of text.
You'll have to note that the second part of the list is not just "things that that IRC doesn't have", it is "things that other stuff does better".
You mentioned file transfers; when's the last time you tried to do anything with DCC? NATting makes that a nonstarter in 2022. What abuse control does IRC give you aside from the ability to block a user (or more accurately, block a host mask, which is probably not even accurate since most servers these days hide those)? Meanwhile over on Discord, I can set it so people can't even message me without adding me to a friends list and me accepting. If someone on IRC wants to make my session unusable, it is not all that hard to do and my options are severely limited.
Discord and Slack and Teams all do threading, file sharing, screen sharing, and I'd be willing to bet that's the top three in the space. I'm not going to entertain the "actual" filesharing Scotsman, you drop the file onto the window and it is made available, which is good enough for most use cases. Not all or most are sharing multi-gigabyte database dumps.
Hard disagree on extensibility. If I want to integrate with discord or slack I don't even have to maintain a client with associated state anymore, I can just provision /commands that callout to a web service. And yes, with modern tooling, I'd rather be speaking HTTP with all the niceties that come with that for free rather than blasting telnet messages over a socket.
Hard disagree on permissions as well. Something like the permission hierarchy on Discord goes as far as command usage and who can even see a channel, and who can be directly notified, not just who can speak or who can kick other people. IRC is objectively more limited in that respect.
I think the main issue is that you wrote "every" there, instead of some, which would have been fine/correct. And that a lot more things in IRC are possible than you realize and some of the modern solutions are somewhat more limited than you state.
Is NAT still a thing in 2022? With IPv6 at home not really an issue anymore (which neither slack nor discord seems to support either...).
Also in the corporate use-case it's not really an issue either.
And wanting to share rather large files is not as obscure of a use-case as you make it out to be (even outside of work!). Of course it's a distribution of sizes and it's nice that the low to mid is covered, but would be nice to have it fully covered.
Every IRC client has ignore and depending on the client that can be very advanced with support for regex and more (slack doesn't have that at all; Discord only has all or nothing blocking; matrix depends on the client; not sure about other solutions).
A lot of the abuse control is server/network side (the same really as with discord, etc.) and really works rather well these days (I see as much/little spam on libera/oftc/.. as I see on slack or discord.. if even that). I would argue it works even better, since Discord has to resort to phone activation to combat spam, while well-run IRC networks manage to be just as spam-free without collecting any email or phone numbers (and just with server-side filtering and other behind the scenes tricks) or without being invitation-only for the most part (which does quite a bit of the heavy lifting as well - which you could do on IRC as well if need be). Some more capabilities very much depend on the network, but you can also limit who can send you privmsgs (for example on libera: everyone; only registered users; only users that share channels; only users that you have explicitly/implicitly allowed). Blocking by registered user names is also possible on many IRC networks - no need to rely on host masks.
If there are things that can be added or improved to improve moderation, people do add them over time - although not in any standardized way, I'll give you that.
Channel operators have more than enough tools at their disposal to moderate discussion and writing IRC bots to do more things that the network doesn't happen to support is trivial.
Modern tooling doesn't always mean better or easier - Getting slack integration to work was so much more pain than hacking up a simple IRC bot to do the same thing.
But just to give you some kind of rebuttal (or mention some unmentioned points by you): IRC has native clients for many more operating systems than any alternatives (many don't even have any native clients at all!). IRC will still work when everything is very broken (DNS on fire, AWS having a moment, ..) and I think a fair few still use it for that reliability aspect. UX is very much in the eye of the beholder. Chatops is very much a thing in IRC as well as adding commands to it (just with ! instead of /).