The newest post on the privacy community on lemmy.ml is 10 months old when viewed on infosec.pub. There are posts from today when you view the same community on any other instance.

Defederation doesn’t remove communities, it just stops updating them. The local copy remains viewable and intractable, but it will not send or receive changes to any other instance. The posts you can see are old posts from before they defederated.

Infosec blocks ml. They are defederated. Lemmy has some severe UX issues related to defederation. Blocked communities look plausibly like extant ones even though they’re not.