I've been a massive user of IRC since the mid 90s... have written lots of bots, scripts etc plus set up plenty of stuff to deal with being able to disconnect your client without missing out on anything (currently use https://quassel-irc.org/ with the daemon on a VPS). I was even l33t enough to "read bitchx.doc" back in the day...
But even I think IRC is a pain in the ass these days. Really the only thing it has going for it is the "openness" of the protocol itself, plus options for clients (although they still pretty much all suck compared to Slack).
But yeah, I prefer Slack/Discord for like 20 other reasons, all of which I care more about than the openness thing.
It's bad enough for casual conversation, but even worse for stuff where you're showing source code examples + screenshots etc. And also stuff were you want to be notified when offline, or read historical comments. Chat systems aren't great for historical searching to begin with, but IRC is by far the worse, unless somebody happens to have posted some logs you want on the web somewhere (and you can find it), which is pretty rare anyway.
It's also super annoying not being able to edit/delete comments.
I know some will hate me saying it... but I really wish a lot more of the older channels related to open source software / programming etc would migrate away from IRC to these newer chat systems.
If people don't like having a company like Slack/Discord in control... fair enough... but there's open source self-hosted alternatives too if that's the main concern.
I'm still on about 50 IRC channels across a bunch of networks, but I wish I didn't have to be. Although I rarely even open my client these days anyway, at least compared to how much I use the other newer chat systems + forums. Half the time when I open IRC I'm not even in half the channels anymore anyway due to nickserv/registration/ping timeout crap that I just can't be bothered dealing with anymore.
Things I've been meaning to write, but didn't:
What I see on the screenshot is that you made everything black and think it's ugly. Customize it. 'IRC on windows' is not a single or even a group of applications; IRC is an internet protocol which just requires a client to connect to.
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I don't think what you want is a dark theme, I think you want an interface designed with CSS. That is a different question than 'wanting a dark theme'- you should know what you really want if you're going to call things ugly.
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https://quassel-irc.org/files/images/snapshot13.preview.png Look into Quassel if you want a bubbly 'modern' interface
Its just something you setup on your desktop or server, so you'd install quassel and run quassel-core connect to it with a client and on the first run the client should ask you to create a new admin login. At least the desktop client does.