I believe it's ban logs that are federated, not the bans themselves, but I don't have any proof. Could someone running a personal instance test this by banning a remote user and see if they can still interact with other remote instances?
Note that if a user is banned by their home instance, it's expected that they can't interact with any remote instance either, as all of their posts will pass through their home instance first.
This link posted there seems concerning. Any individual instance can issue a federal ban? https://lemmy.pineapplemachine.com/post/5781
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