I don’t see how you can hold these two positions simultaneously.
They’re about different things. One is an opinion about bottom-up, community activism and the principle of self-determination, and is a belief that exists independently of the material conditions and reality of global politics. France only supported the Americans in order to “get back” at England. They later regretted it when the Americans supported the French Revolution. When I say I support separatism, I am thinking specifically about how Lenin released all of the Russian Empire’s colonial nations, regardless of how it might adversely impact the Soviet states’ security prerogatives.
If part of a country wants to leave, and the government of that country says, “No, and we’ll use force to stop you,” and another country says, “Hey, seperatists, we’ll support you,” then where do you stand on all that?
Like I said with France and the 13 colonies – no country is actually saying that or has ever said that. France didn’t go “yeah, we love what you’re trying to do 13 colonies and support your beliefs wholeheartedly”, they went “oh cool, this will help us regain New France one day and really piss off our archrivals.” Likewise, Russia, having lost Ukraine (and the Eastern Bloc), is trying to regain its lost glory, and it just so happens that they can exploit Donbas separatism in order to do so.
My understanding of the Donbas is that it was largely populated by Russians from the Russian SFSR during the era of open borders within the Soviet States, which also makes things different than Catalans, Kurds, and Scots, for example.