You can actually move a car, or get it to bounce or rock slightly if you rock back and forth in the back seat hitting the seat back with each oscillation.
But, you have to have intermittent, not steady pressure.
This appears to be the same thing. The trick is that the microwaves would be acting like, for lack of a better analogy, someone firing a pistol into a trap on the from of the car. The bullet could, if it had enough kinetic energy, transfer energy to the trap and move the vehicle. With a pistol that energy would be balanced by the recoil.
The microwave generator has no recoil.
At least that is how it appears to me.
Not so. On high-power communication satellites with large asymmetric transmit antennas, pumping out kilowatts of microwaves requires continuous attitude compensation to counteract the recoil. Recoil of course happens on all comm satellites but at low power and with reasonable symmetry it becomes a lower order factor.
But, you have to have intermittent, not steady pressure."
I believe that Bill Clinton has tried this experiment in his old El Camino many times.
Sorry, if the pistol is mounted or held inside the vehicle, the same force of the bullet moving through the air and or hitting a solid plate will be offset by the recoil moment ( equal and opposite force). So, no joy there. Same for rocking back and forth- in a car etc the same amount of energy is applied in both directions. That’s the thing about the laws of physics- they are really hard to break. some old white guy made us all subject to them....