Being genuinely anti-imperialism, anti-colonialism, etc. means that you're that way across the board, no matter who is doing it. You don't whitewash the Ottoman Empire or Japanese imperialism just because they weren't "white" in an American sense (and in Japan's case, buy into their own propaganda, as they used the specter of Western imperialism to justify what they did to other East Asian/Pacific countries). You don't make excuses for modern Russia trying to take over Ukraine or other sovereign natures in Eastern Europe. If you truly believe in self-determination then it doesn't matter who is trying to prevent that. This shouldn't be hard, right?
Putin went on Russian television today saying that Ukraine belongs to Russia because it was Russian territory during the days of the empire. There's absolutely no anti-imperialist theory that would applaud him for that. None.