Afaik, you actually can’t, at least for now. You can follow everything from Kbin though.

From my understanding, Lemmy is software, while ActivityPub is the underlying protocol. Mastodon, Pixelfed and Kbin are other softwares running with the ActivityPub protocol.

Jerboa has the setting you request under Settings > [username] Settings > Hide Read Posts

That must mean ActivityPub tracks read status and provides it. Just look deeper in the settings.

Sorry, I don’t know about Liftoff.