We know the obvious racial policy differences. But, since you're throwing around terms, broadly speaking the economic differences are surprisingly sparse and both of whom nationalised a lot of Italian/German industries and, broadly speaking state control, state planning and centralisation of the economy is something we associate more with 'left wing' (statist) economics.
Why do you think think people describe the political spectrum as an 'inverted U?' It's because if you take 'Marxist' USSR under Stalin and 'fascist' Germany and Italy, you see a lot of similarities.
How you come to the conclusion that Trump is a 'fascist' is beyond me. If you want to accuse of him of having 'dictatorial tendencies' or being 'authoritarian', we'd find some common ground. Fascism is a specific set of principles that, frankly, Trump does not hold. It's just as ridiculous for anyone to call Kamala Harris a 'communist' or 'Marxist'.