The reason people critically support Russia is for that exact reason

any leftist who opposes a mutlipolar world and the weakening of US-NATO, most likely lives in the Imperial core or one of its vassal states. They have no problem with the US being the lone superpower with the ability to crush or starve any country that tries to implement a more equitable system that goes against the US "rules based order". With the rise of China and Russia and the weakening of US-NATO, countries like Cuba, Venezuela, DPRK etc, will have breathing space to chart their own path, instead of being constantly under the jackboot of US Imperialism. Just look at the recent Cuban energy crisis, which countries sent aid? Russia, China and Mexico. Is Russia sending this aid due to past socialist relations? Nah, but instead of constant US led colour revolution attempts, that some Western "leftists" have no problem with and even support, stability in these countries is geopolitically better for Russia-China.

Critical support means supporting a nation fighting back against the other nation that has a global hegemony economically and in military as well against their proxies. We acknowledge that the Russian Federation is an oligarchy; but unlike America it doesn't have military bases surrounding and in every country around nations they are hostile toward nor dictates the actions and policy of the west which is the primary aggressor and agents of imperialism defined by Lenin.

Despite the death of the Soviet Union, it still has done more for the international working class than any settler project.