The GetInvolved section of the GNOME wiki indicates that GNOME is moving from IRC to Matrix. Issue #147 describes that the built-in help needs updated to reflect this.
Adds a new page giving step-by-step instructions for users new to Matrix and moves the IRC and mailing list pages to a new "legacy platforms" guide page to prevent unfamiliar users from clicking them. Also adds a link to the Internationalization team's Matrix room on the translate page.
Does not address Discourse. I'm not sure how to add Discourse or how relevant it is to a new user seeking support as it contains mostly dev and admin stuff. Internationalization also doesn't seem to have a presence there.