Are superhero comics propaganda for the US? https://en.m.wikipedia.org/wiki/United_States_propaganda_comics
Some are.
Captain America beat a Muslim terrorist to death after 9/11.
No, because propaganda implies it was created by the government to promote itself, whereas almost all superheroes were created by people unaffiliated with the government.
Times they've appeared to be, such as characters battling in WWII or fighting communists or other US enemies, it's usually because of a) the creator's own frustration with these enemies or feelings of patriotism or b) pressure from outside to promote these feelings in order to distance oneself from those enemies or for financial reasons.
Not anymore.