What do you think Federate means? It absolutely does, Matrix Federates over the Matrix protocol, which is a separate protocol from Activitypub which is what Lemmy and Mastodon use. It doesn’t Federate with Lemmy and Mastodon because they are different protocols but it absolutely does federate. Honestly there’s no reason for it to Federate with Lemmy and Masotodon. ActivityPub isn’t a good protocol to use for chatting, Matrix as a chat protocol is superior. Not to say that activitypub is bad, it’s great for social media platforms like forums and blogging, it’s just not good for instant messaging.