Difference in lift generation for a swept wing and straight wing in subsonic condition
Since both the lift curve slope and the effective angle of attack are reduced by the cosine of the sweep angle at quarter chord, the lift coefficient of a swept wing at the same geometric angle of attack is reduced by the square of the cosine of the sweep angle.
Also, the pressure distribution over chord differs between straight and swept wings, especially near the center and the tips. All this makes swept wings less attractive, were it not for their ability to delay compressibility effects, basically for the same reasons which reduce their efficiency.
However, lift is generated in the same way: By pushing air down or by a pressure difference between upper and lower wing. Both are equivalent explanations of lift.
Only at high sweep angles and high angle of attack will vortex lift kick in and produce this pressure difference by means of a strong vortex on the upper side of the wing.
Since you ask about &quot;subsonic condition … lower than Mach 3&quot;, I wonder whether you actually ask about supersonic flight with a subsonic leading edge. Now things are rather different between a swept and an unswept wing: While the sufficiently swept wing with a subsonic leading edge will still exhibit a pressure distribution similar to that at subsonic speed, the supersonic straight wing will create a shock, resulting in a slowing down of the flow where at subsonic speed an acceleration could be observed, and vice versa. Also, the center of pressure will move back in supersonic flight.