If any of you is curious about how best to block #Meta #Facebook #Instagram or any other faceless corporation from interacting with your posts on Mastodon, you(r admin) will want to look at turning on AUTHORIZED_FETCH for your instance. This setting, partnered with a bog-standard suspension of an instance, ensures that your posts won't leak to that instance via transitive boosting.

It works just fine. I've had it turned on on Old Mermaid Town since almost day 0, and we federate with other instances, even other fedi software, just fine*.

* Almost. We found a weird follow bug with Bookwyrm which we are still trying to identify.