One of the things I use Discord for is the Heroic launcher server, mostly for the channel where "Gaming on Linux" news is posted.
They're investigating Fluxer as an alternative. So, I popped over, created an account, muted everything but that one equivalent channel...
... and, hmmm, I'm not sure how ready Fluxer is for this. I mute "until I turn it back on" an entire category and yet still get activity dots for the channels.
And they seem to have somewhat limited keyboard navigation (I'm used Shift+Alt+<up/down arrows> to navigate to "next channel with unread messages").
I did do a quick search to see how good Fluxer might actually be, including things like security response, but didn't come up with much. They have some form of bug bounty program, but looks like the only rewards are "kudos" and maybe some free month of their premium sub.