@catppuccin#SourceHut is free software and has CI capabilities. Discussions in email have worked fine for decades, and still works for quite large projects.
As for real-time chat, #IRC still exists, and doesn't even need me to register an account to ask a question. There's plenty of good webclients to keep the barrier lower than Discord could ever do. Creating a bot for IRC is perhaps one of the easier tasks an aspiring programmer could work on. I have no clue what "forum channels" are supposed to be, but I'm quite certain it is not a required feature to develop software.
It seems incredibly bad faith to pretend these things don't exist or aren't known about.