One of the benefits of the fediverse is that there is no over-arching code of conduct, precisely because there’s no way to enforce it. Each instance’s owner decides on what they are willing - and not willing - to host on their own instance. Other instances can “defederate” from yours if they don’t like what’s hosted there, which means the two instances will stop talking to each other, as beehaw did with lemmy.world. But there is no way to globally ban an instance off the face of the internet.