I actually came up with a good scientific explanation for how Superman can fly. He physically does it. He physically moves the atoms of his muscles to provide motion towards whatever direction he wants to go. That changes the mass of his body to provide lift, direction, and speed. I haven’t seen this idea anywhere online.
You know how sometimes you have dreams when you fly?
This is exactly how I fly in my dreams.
I just thought earth life gave him gastric problems.
When I have that kind of dream I don’t fly so much as levitate and glide along at a slow pace instead of walking. And for some reason it always takes ***INTENSE*** concentration on my part, a supreme act of will to leave the ground.