FYI, I've already submitted this as a feature request on the Sync for Lemmy GitHub.
Blocking is already a Lemmy feature. We're talking about accessing a Lemmy feature from a Sync menu. A useful feature that has already been implemented on other clients (Liftoff) and it is great if you tend to see a lot of content that you don't want to see, which I feel is probably a lot of us.
Technically Twitter has recently become available lol.