Most moderation is done by individual communities, not instances. You want an instance that's unlikely to defederate with another (basically blocking it). Think of a community as a subreddit, and each instance as a server holding a cluster of them (and usernames). Thanks to the magic of programming and federation, the instances typically work with one another to make it more seamless.
My understanding is that lemmy.world is not prone to defederation. Vlemmy.net had a similar policy but they seem to have gone under a few days after Reddit went stupid.