I've mainly just seen in on the lemmygrad instance when I go to all. I find the content over there to be a bit silly (even as a socialist). I think you can block instances? I've blocked some of the more trolling/low effort communities.

But I also see it in the other direction. I've seen people ask open ended questions about the USSR and CCP for something they may have done well and people will downvote and "what-about-ism" for other stuff that isn't/wasn't so good, but is also off topic for what was asked.

There's not a lot of effective discourse around the topic, I think. The conversation seems to be either entirely positive or negative for everything about them, even when the post is about one thing in particular. We can't really say, "This thing was done well" without the what-about-isms, nor can we say "This other thing was not done well" without it applying to everything.

But to come back to your question, as you worded it "support for...", that seems to be in line with the conversations here. It's either "support" or "against" and not a whole lot of analysis. As in, if you say something positive then you support everything. Obviously, that shouldn't be the case, but that does seem to be the narrative here.