IANAP but it seems like it would be trivial for a client app to do. Look at the combined vote weight (e.g. -8 + 4 = -4) and if it's below user inputted threshold, don't display it.
That said, Lemmy isn't Reddit. When I see a post with a negative score, I can sometimes see why it's not popular, but it's seldom straight up garbage, and I can still vote accordingly. Never used the feature on Reddit because I've been brigaded by entire communities for acknowledging that their favorite show's latest season exists (it's not Game of Thrones, but similar energy), and I don't think people should have the right to censor others; I believe each person should have the right to choose what they see.