how to block meta from mastodon

They literally announced their intention to federate, friend. One of many announcements. See the section "Compatible with Interoperable Networks." ActivityPub is the open source protocol underlying lemmy, kbin, mastodon, etc. This is totally an EEE situation - a corporation only says "we'll let you leave us" if they intend to dominate the fediverse to the point that leaving is painful to the user. Which means they're going to fuck the standard or do other strategic action to fuck the fediverse.