IRC + Jitsi could work for a lot of people, but there's still enough trust in big centralized platforms for people to be satisfied with them.
https://github.com/ergochat/ergo
a. Ergo [1] as the server for a greenfield setup
b. Gamja [2] and Goguma [3] ) as clients
c. Soju [4] as a bouncer for non-Ergo networks
[1] https://github.com/ergochat/ergo [2] https://sr.ht/~emersion/gamja/ [3] https://sr.ht/~emersion/goguma/ [4] https://sr.ht/~emersion/soju/
It's common for IRC users to use IRC from a terminal client on their desktop. If they have a remote server they'll ssh into a box and use their terminal client there. They'd also use a screen session to keep their IRC client running 24/7 so they can keep receiving messages. Or they'll keep an eggdrop bot on a server somewhere, which is basically a sorta IRC proxy that they connect to from any IRC client and can keep their user online in the background.
Here's some stuff on IRC: https://github.com/ircdocs/modern-irc | https://ircv3.net/ | https://wiki.wireshark.org/IRC
Looks like there's some discord<->IRC gateways: https://github.com/sjwhitak/discord-irc-matrix https://github.com/qaisjp/go-discord-irc https://discordrc.com/
Here's some IRC stuff in Go: https://github.com/khlieng/dispatch https://github.com/ergochat/ergo https://github.com/go-irc/irc https://github.com/search?q=go+irc