To attempt to explain this without using the ‘critical support’ formulation, it’s not necessarily ‘support’ of Russia in as much as it is supporting the prospect of your own state (whichever that may be) failing to advance its war goals so that instability (and thus a potential path to a revolution) is created. I personally don’t look at Russia as some kind of darling, but if the West proxy-war stomp them that isn’t any good for the prospect of conditions changing in any way that supports raising of class consciousness, worker organisation, and eventually revolution. (Not to mention the threat of a frankly very much more erratic Russian Federation potentially using nuclear weapons, which is a complete failure state for humanity)

Russian communists should be anti-Russia, western communists should be anti-West. (ex: Russia loses, is destabilised, creates better conditions for revolution there. If Russia keeps this going for a long time, the West keeps bankrupting itself, causing internal strife, creating better conditions there) If that makes any sense.

With regard to sympathy for Ukraine, it is kinda like… the US is absolutely going to drop Ukraine like a toy they’ve gotten bored of the moment that war goals are achieved (and this is already happening with Europe pivoting away from Russian gas and toward US LNG exports). In a scenario where Russia is defeated, you can already see US capital rubbing their hands together in glee for all the exploitation they can do “rebuilding” Ukraine in their own image.

I personally think a lot of people get a bit lost in the sauce trying to pick one side or another to “support” when the answer is to be against your “own” side, which sometimes looks like “supporting” the other side.