It’s primarily the Tankie Triad; That’s .ml, hexbear, and lemmygrad.ml. To a lesser extent, some people also include lemm.ee too. The reason tankies are so widespread on non-communist posts is because .ml is the Lemmy dev’s home instance. So if you want to see updates for lemmy’s development, you need to federate with .ml. Which means even non-tankie instances are inevitably exposed to all of the tankieposting.