You asked — “Why is there so much propaganda against him (Hitler)?”

ALL powers demonize and defame their enemies. It’s how they get their own soldiers to disassociate the enemy soldiers from their humanity so their own soldiers will Kill them.

Germany and the National Socialists got an Extra Heavy helping of this from the jews who were doing their usual parasitic thing in Germany in the 20’s and came close to installing a Communist government. Hitler and the National Socialists pushed back. The Jews declared war on Germany and the rest is (distorted) history. The Jews invented extreme atrocities like “The Holocaust” to use as post war political weapons to justify things like stealing Palestine and killing and ejecting many of their people to found Israel. They have played the “muh Holocaust” card for decades for reparations from the Germans even up to the present time. They are heavily invested in this WWII atrocity propaganda and strongly defend it.

Side Note —. You can see how the leftist (jewish) media very effectively played their “Hitler Card” against Donald Trump the Nationalist. Attaching and associating Donald Trump for 4 YEARS as being “literally Hitler” and being a “Nazi”. Once you convince someone of things like that then they will gladly break election laws in order to get him ejected.