In my experience this often has to be phrased as “Discourse, not DIscord. It’s a different thing. And actually Discourse was there first.”
Which is not very concise.
For what it’s worth, I say “forum” or “discussion forum”.
I named discussion.fedoraproject.org that from an old sysadmin rule of “never name a service after the software”. But, the folks from discourse.gnome.org told me they picked that on purpose because they want to highlight and give credit to another open source project — which is a fair point.