Unfortunately, if they were to do this I’d imagine they’d be able to know you blocked them - as your instance would need to tell the other instance (and if they were a single user instance they could grab that record from the database) to hide your comments/posts. Which could cause even more problems as there are definitely people who’d go scorched earth over it. Even if they didn’t go on a rampage about it, they’d still be able to just then logout and see what you’re saying because of that.
From what I recall in the ActivityPub spec, transmitting blocks is already there, but I imagine no one implements it for that reason.
And additionally, to the community at large - admins, moderators, people who post/comment - we all have played a major part in expanding Lemmy and the Fediverse in general!