4 pane comic of dolan on the left and spooderman on the right
pane 1 (dolan): cum join opensurce cummunity!
pane 2 (spooderman): shure! how joyn?
pane 3 (dolan): Here discord! (with discord logo)
pane 4 (spooderman with tears in eyes): y u do dis?
Matrix is the best platform IMO, and actual dev communities agree. (See: Github, Mozilla, KDE, Nix, the list goes on)
This is in addition to forums, git, wiki, etc, which those communities also provide.