what I was taught (and what still works for me) is to look out the front window, never the sides, and pick a as far away (ideally on the horizon) to focus on.

the theory being, at constant velocity in a straight line, your body feels at rest, so you want to look somewhere that reinforces that. looking out the side window has scenery rushing past, which is the opposite.

turning sideways and reading sounds like a nightmare.

How can you look out the front window at the horizon and be reading at the same time? Somewhere in this thread we've confused generic car sickness with reading while in a car.

This. Obviously, it doesn't help you read but if you're bad enough that just being in a car makes you sick it helps a lot. When I was younger any car sick kids got to sit up front and there were a couple of adults who had to be the driver for the same reason. I still get bad on boats and the only thing that has worked is to find somewhere to lie down and close your eyes for the journey. Makes a big difference on a ferry. Not as effective in smaller boats.