@Jeruba I think The Trump Prophecy is the closest example I know, not as explicitly pro-Nazi, but considering the various ways Trump has given tacit support to white supremacists and facism in the USA, any film elevating Trump as a positive figure who ought to be in charge of the USA seems like it’s pretty close to what the question was asking for. ( supporting meme )
I intentionally chose that and Triumph of the Will with a little dark humor in mind, but also as an implied answer that no, no explicit pro-Nazi film comes to mind that would be a cause of American Nazis.*
I don’t think Nazism generally gets caused by films. I think it is better understood as one type of alignment with racist/anti-semetic/xenophobic and facist tendencies, which have various origins and sustaining/encouraging groups and patterns of ideas, which overlap with some groups/ideas that also identify as conservative, or Christian, or capitalist/anti-socialist/communist, or American. ( supporting meme) )
In many cases, it seems to me that many people who become neo-Nazis and/or white supremacists are mainly very ignorant, isolated, disturbed, and paranoid people who profoundly don’t understand WTF they are angry about.
. . .
* On the other hand, there are an increasing number of videos on the Internet which are various flavors and combinations of conservative, QAnon, Y’all-Qaeda, Republican, white supremacist, and/or neo-Nazi, which do no doubt generate and reinforce a lot of support for those groups, including neo-Nazis. The actually pro-Nazi ones are probably rarest because they tend to be vulnerable to removal by hosting companies, but YouTube is crawling with videos and comments that are supporting views allied with the groups I mentioned.