You shouldn’t need any dedicated RAM. A decent microcontroller should be able to handle transcoding the output from the camera to the display and provide infotainment software that talks to the CANbus or Ethernet.
And the bare minimum is probably just a camera and a display.
Even buffering a full HD frame would only require a few megabytes.
Pretty sure the law doesn’t require an electron app running a VLM (yet) that would justify anything approaching gigabytes of RAM.
So what microcontroller do you have in mind that can run a 1-2 megapixel screen on internal memory? I would have guessed that a separate ram chip would be cheaper.