Yeah, I know

I’m not a mechanic but my much older brother is and I’m very technically minded.
I’ve got a private pilot’s licence and work in the nuclear industry. I’m not saying that to big myself up, but it’s pretty obvious the cause of the problem is not something a steering damper will solve (though I’m hopeful as I don’t want the hassle and want to be wrong!)
It feels very much driveshaft or motor related. Speculation; but if one of those was out of balance and then started resonating it would explain why acceleration makes it worse and it doesn’t stop until under a certain speed.
Steering dampers will just mask the feeling through the steering wheel but I can feel it through the whole car and hear it too. The most expensive problem is a motor out of balance. My guess is the rear motor is different to the other models (since drive mode has no effect and the rear motor is always engaged), it has a common defect and is way too expensive to replace. The factory fix was probably not on the vehicle production line but a change to the motor production line.