theoretically if an alien from another exoplanet with a much stronger gravity from ours comes here could that alien be able to levitate/fly on Earth?
No, not any more than being born on Earth gave astronauts the ability to levitate or fly on the Moon. Coming from stronger gravity means you’d need to be stronger to move around, and you can jump higher in lower gravity—but the law of gravity applies to you nonetheless.
If the alien was humaniod and as far as we know it would be, no! The alien might have stronger leg muscles an jump higher but earth’s gravity would have the same effect on them.
No. Gravity means any object will still fall toward earth.
Now, if the aliens body was less dense than the earth’s atmosphere, then it’d float like a helium balloon. But that has nothing to do with the gravity of its home planet.
You can imagine animals from earth on a planet like Mars or even our Moon. Animals (and humans) capable of jumping will be able to jump higher due to less gravity. However, they will still land on the surface of the moon or mars. And because the moon doesn’t have any atmosphere and the mars has very little, birds and insects that fly on earth will not be able to fly at all.
It is not different from when humans visited the moon with 1/6 the gravity of earth,. Humans on the moon could jump higher and carry more mass than down here on earth but not fly or levitate. The astronauts were limited by stiff and heavy spacesuits.
As long as there is any gravity to fly or levitate you need to be able to apply a fore to counteract it. So you need wings or something similar to create a downward force. So at best, the aliens would be able to jump very high and very far but not fly.
There might be an exception and that is if you could jump so you reach escape velocity. You would then be able to jump and orbit the sun or the object you jumped from orbited. I would not call that flying or levitation. Humans could do that too on a small enough object like a comet.
From earth, you need to jump at above 11.2km/s, the problem if you could is to survive the forces from the air and not be evaporated by the generated heat.
What makes you think that? An alien from a higher gravity planet would have to be much stronger and stockier to support itself. Think of it like a submarine on earth: it’s built to be neutrally buoyant in water, which is a lot denser than air, just like the atmosphere on a higher-gravity planet would be. There’s no way in hell you could get it to fly because the wings it would need would create too much drag in the environment it evolved in. Or like an elephant transported to Mars. Massive is still massive.
Could this creature jump like a beast though? Maybe. But probably not to truly fly.