Lift is created by the differing pressures between the upper and lower
surfaces of the wing coupled together with AOA.

Wings generally tend to have a curved suface. The upper surface has a
greater arc or curvature than the lower surface. As the air flows across the
surfaces of the wing, the upper surface air is forced to move faster than
the lower surface air thus causing a pressure difference between the two
surfaces.
The pressure difference coupled together AOA is what causes lift.
On the question of wether the wing is 'pushed' or 'sucked' into the air, as
far as I am aware the jury is still out on that point. Personally I
subscribe to the view that it's probably a bit of both.

As for air density, that is another point. as you will be aware that air
desity decreases with altitude i.e the higher you go the molecules are less
densly packed which is why any wing has a maximum service ceiling, i.e the
point at which it won't generate any more lift. It's also worth noting that
VNE decreases with altitude.

Glider pilot.

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