Yes - -for certain values of SF. Nobody is going to call the MCU hard SF, and superheroes are a fairly clear genre of their own, but in the broadest sense that genre certainly feels like it fits into the overall category of SF.

Marvel crosses many genres depending on what heroes your talking about Broadly speaking it best fits as fantasy examples Guardians of the Galaxy is definitely scifi so is Thor Ragnarok while captain America winter soldier is spye fantasy