People, just a heads up: ASB specifically means TLs with supernatural, extraterrestrial, and geological intervention in a TL, it does not means "extremely unlikely to happen", I shrugged off this timeline when it appeared on the main page, but now it has actually made me interested in such a scenario, even if it is comically impossible.
The only POD that I can see in here, is Hitler becoming a hardcore Communist before WW1 instead of a German Ultra-Nationalist/Aryan theorist, befriending Stalin, Trotsky, and/or Lenin, and eventually moving to Russia and aiding the Bolsheviks during the Russian Revolution, but even if Gitler is a Communist living in Russia ITTL, something would need to prevent Stalin from rising to power, and Gitler from quickly rising the ranks instead of Stalin and anyone else. the evil genius Gitler snatches a plot to poison both Stalin and Trostky, usurping the throne of the Red Tsar for himself!
(let us refer to the Soviet Hitler as Gitler with a G for convenience, with Hitler with a H being his OTL self, however, ITTL I can very much imagine Gitler ditching his birth surname altogether and choosing a new pseudonym for his revolutionary persona, like how Vladimir Ulyanov became Lenin, Ioseb Jugashvili became Stalin, and Lev Bronstein became Trotsky)
And about OP asking if Hitler would become a racist Slavic/Russian Nationalist instead of an Aryanist, he could very well continue being a genocidal racist as he was IOTL, but him being a Pan-Slavist instead? I don't think so, just think for a bit: the leader of Russia/the USSR is himself an ethnic German/Austrian who does not even comes from the historical German minorities of Russia (like Volga Germans, Baltic Germans, Caucasus Germans, etc.), Gitler is a full-blown foreigner who immigrated to Russia, and somehow managed to become its leader, at least for Stalin, while he was an ethnic Georgian, he was born when Georgia had been a part of the Russian Empire for a long time, and his contemporaries saw that Georgia would remain a part of the USSR forever.
ITTL, the USSR under Gitler could be more internationalistic and appeal towards world revolution, disregarding Socialism in one Country or at least its OTL variation of it, since the USSR's supreme ruler was not even born and raised in Russia nor any of its republics, and (apparently) he has only lived in there for around 11 years, with the foreign-born Gitler wanting to show to the world that the USSR is not a result of Russia falling to Bolshevism due to Russian problems, but the entire proletarian world wanting to unite under the same banner.
The only way for Hitler to become a Pan-Slavic Nationalist would be if he pulls a Stalin and attempts to disregard his German-Austrian origins in exchange for him identifying as a hardcore Russian Nationalist, but again, unlike Stalin, Hitler is a foreigner who has lived in Russia for around only less than a decade, it depends what this Gitler is doing as the new leader of the USSR, if he wants to showcase the USSR as the first steps of the international revolution, or of it is just the Russian Empire with a Communist cosplay, I find the former one much more credible and less forced than the latter scenario.
In the alternate history wikia/fandom back in like 2012-2013 there was a TL where shortly before his birth in 1889, Hitler's family immigrates to the US and he is thus born and raised as an American citizen, he eventually becomes the President of the US during WW2, with Himmler as the Fuhrer of Nazi Germany instead, I can vaguely remember that ironically, ITTL US President Hitler nuked Germany instead of Japan.
I also think that his nickname was "Andy", or that was maybe my head-canon back then, I thought that this TL was awesome back when I was still a young teenager getting into alternate history but now the more I remember of it the more goofy and nonsensical it is.