For you, @SlimyRat@lemmy.ml as a lemmy.ml user, lemmygrad.ml isn’t blocked, search for lemmygrad on https://lemmy.ml/instances to confirm. Other instances (like beehaw and sopuli) did defederate with lemmygrad. Lemmygrad is a topic-oriented instance (or at least an instance with a very strong cultural backdrop) of radical leftism. Not the mainstream liberal progressive left, but like Marx, Lennin, socialism, communism, radical anti-capitalism. Users on instances with cultures that lean in liberal progressive directions often clash strongly with users from this instance with a strong radical left culture.

This culture clash regularly causes flamewars and moderation shenanigans. As a result, some instances defederate with lemmygrad. But again, lemmy.ml is not such an instance and lemmygrad is not blocked for you.