@Avner @dansinker @levy neither, it is a *server* feature of mastodon. so you mute via talking to Mastodon over the Mastodon API.

ActivityPub supports things like Block and could support a Mute activity too but afiak nobody does the latter (I think because muting is something that you naturally only track yourself and don't advertise out to the world, so federating it would be pointless)