Formerly chapo.chat and r/chapotraphouse, they are a tankie instance that frequently brigades threads that mention them, and engage in harassment campaign against anyone who disagrees with them. They also frequently praise and defend Russia and China, two genocidal dictatorships in which one is engaging in an illegal war against ukraine and china has rampant human rights abuses. Since there are good faith users on that instance, they are more of a hesitation than a censure.
This isn't reddit. The whole point of federation is that different instances can interact with eachother.
This really shouldn't be hard to understand.