So many folks on here are jumping on and claiming that decentralization is a one way or that people don’t know anything, but have failed to read the specifications themselves.
ActivityPub defines the Block activity for client-to-server (C2S) use-cases, but not for server-to-server (S2S) – it recommends that servers SHOULD NOT deliver Block activities to their object.
So as I mentioned before, Lemmy.world should be blocking those servers at the instance level, preventing it from sharing any data to any identified Facebook instances.
Sure this doesn’t stop Facebook from spinning up other instances, but that will improve a lot more effort on their side and will quickly be identified and blocked by the communities, just like all their urls for ads, api, etc. have been for years.