There's a difference between European nationalists and American racists
During the ongoing war, the pro-Ukrainian position is broadly shared by almost the entire Finnish society from left to right, apart from small groups of conspiracy-theory oriented movements. Even those who continue to, say, oppose Finnish Nato membership or who would prefer an immediate ceasefire in Ukraine do so from a viewpoint that condemns the Russian invasion and considers the goal of the preservation of Ukrainian broad sovereignty to be important.
Naturally, far-right Finnish nationalists would also be pro-Ukrainian, often fiercely so, with the aforementioned conspiracy-theory movements excepted. However, in an age where conflicts are also fought on social media, this creates problems for international cooperation. A thing that has caused a some such Finnish nationalists, particularly those of extremely-online variety (not a movement I belong to, naturally, but one I follow with great interest) to recently become very negative about the American alt-righters is how a great number American alt-righters have become Putin cheerleaders in the Ukrainian war.
There's more to this anger than just American alt-righters being pro-Putin. After all, nationalists aren't automatically allies, often very much the opposite. Nationalists from different nationalities might have different national sympathies. It's the sheer gumption of American alt-righters like Bronze Age Pervert to argue that Ukrainians are *stupid* for fighting for "globohomo and a Jewish president" and such things, and should just surrender to Russians and let Russia occupy them and cleanse them of the Western taint, as if this was somehow obvious.
To Finnish nationalists, this seems not only wrongheaded but incomprehensible and cowardly, as if ephemeral ideological concepts like "globohomo" should be put before the primal nationalist attachment to defending your blood and soil from a foreign invader, let alone an ancient enemy (of both Ukrainian and Finnish nationalists) like the Russians. Posts like this one showcase the attitude.
Many people that consider themselves "American nationalists" don't really fundamentally "get" nationalism the same way as Finns would understand it. Such American nationalism is not really as much nationalism as it is racism, combined with reactionary attitudes about sex and homosexuality and so on. When I say “racism”, I do not just use it as a general moral condemnation but as a name for a real ideology, one that believes not only are there human races but the differences of these races are basically the most important thing there is for understanding politics, or at least one of the most important, and political decisions should be made on the basis of these racial differences.
In other words, while a nationalist would be most concerned with defending one's polity from other polities, a racist would instead be conncerned making sure that one's own polity consists only of one's own race or at least in a great majority, openly discriminating in favor of one's own race compared to others etc.
Of course, European nationalists can well be racists as well, and often are, defining their nation in a way that by definition excludes nonwhites from it, even if it might tacitly include white people of differing ethnicities. Likewise, there exist American nationalists whose nationalism is based on integrating or rather assimilating various peoples to the general American identity, whether those people want to be assimilated to not.
However, since such American nationalism tends to be race-blind at least in theory, openly racist “nationalists” don’t really belong within its sphere. Even their use of American nationalist symbology seems connected to this - "the left says Founding Fathers are racist? Damn right they were, and we love them for it! Here's pictures of George Washington, who was BASED, etc."
Thus, in a sense, this racist perspective ends up, in a way, being *more* tolerant than a more strict nationalist perspective. It not only contains an explicit appeal for discriminating against different races, it also contains an implicit belief that all the people of the same race (here: white) should unite, "no more brothers's wars" and so on, just because they're of the same race. In this way, it might make sense that Ukrainians should indeed let Russia conquer them again - what does it matter if they can't speak Ukrainian, teach their kids Ukrainian history etc. if they're still all white?
And if one has managed to start believing that Russia is actually a traditionalist nation, based country, perhaps even a potential ally of white nationalism and so on, it would actually start to sound appealing that Russia could be made as strong as possible, perhaps even so that they can "liberate" other countries from the clutches of rainbow flags and immigration. Of course, an nationalist from some country from the Russian borderlands, a country that used to be a part of the Russian Empire, would see things very much from the perspective of another country that was a part of the Russian/Soviet empire even longer.
Of course, various atrocities have been committed both in the name of racism and nationalism, and it’s questionable how valid a perspective either of them are to what’s happening in Russia-Ukraine or elsewhere in the long run - after all, it’s a fair guess a big reason for the current invasion is Putin really starting to believe all the Russian imperial-nationalist myths that his regime has been based on for decades.
Likewise, there may be multiple reasons for why far-righters might look towards Russia - admiration of authoritarianism, general belief in Russia continuing to be a bulwark of reaction, but perhaps above all simple enemy-of-my-enemy-is-my-friend idea of both Russia and them being on the same side against Anglo-American liberalism, globalism and such elements. Still, looking at divisions like this may provide more extensive clues about ideological faultlines and future developments.