I didn’t even know there was a Gitter chat I agree, no need for IRC, it’s merely a dev flex That being said, GitHub Issues is out of scope.
As for GitHub Discussions and Discourse. I’m not sure where we are currently getting more user action.
I think Gitter (or Discord) and Discussions would be my go-to. Discussions would be a more common place for implementation/help I think and Gitter/Discord would be more a community thing.
Seems like most projects use Discord now instead of Matrix, IRC, Gitter, Slack, Zulip, etc.
I will add that Discourse has a nice weekly feed. We’re hoping that GitHub comes out with something similar. (Email digest · Discussion #4075 · github/feedback · GitHub)