I don’t know what discord is, but I find that every social media owner/admin and developer can be reached at discord. Another thing is Matrix.
I’ve got no clue about these two platforms but I believe that they’re not a part of the fediverse.
I very much wish that replicas of these were available on fediverse, so that we could interact with them from our Mastodon, lemmy or other Fediverse handles.


Matrix is basically federated Discord based on an open standard. But it’s a separate thing from the fediverse.
The thing is that Matrix and Discord are really intended for real time chatting, including private and encrypted chatting, in a way ActivityPub isn’t (which is more about persistent public conversations). So it makes sense that they are separate things.