Instances can ban you without others being affected. Your comments could be visible on one instance and not on another, so there’s a level of shadow banning going on.

Real shadow banning isn’t implemented in Lemmy. It could be, but it’d only work for accounts on the same server. It’d also be pretty easy to detect, although the same also goes for other places that do effectively use shadow banning to fight trolls and bots. The people shadow banning works against aren’t smart enough to verify that they haven’t been caught in the first place.