In your video you can clearly see that the camera is moving relative to the window, a mount that fixes the camera solidly to the glass will solve the problem and will be better than using EIS. The only time EIS is useful on a large vehicle is if you are completely off road climbing over rocks. For a motorbike EIS is more use and for a bicycle it is essential, but on something as heavy as a car it is much better to use the car suspension for the stabilisation. That mount looks OK, your quadcopter one probably wont work, its designed to remove the jello from high speed spinning propeller blades.That's an excellent point. I have never done so with my action cams and perhaps that's the cause.
I have ordered this mount and will see if it solves some of the vibration issues. .I don't know why it says suction mount since it is stuck in place with 3M double sides tape. They sell this mount for SpyTec dashcam/camera for 8-9$ on Amazon and Ebay.
https://www.aliexpress.com/item/Car...101.html?spm=a2g0s.9042311.0.0.218d4c4dXkbFhZ