Thank you for this insight! I will contact the dealer of the lift kit about those extra parts or any other recommendations.

Thanks also for helping me with the correct words for these parts! Yes I am asking about the control arms (product link), and yes the rear control arms do have eccentric adjustment bolts, but adjusting these to their minimum isn't sufficient according to the shop, and more-eccentric bolts don't exist.

It seems that the toe-out comes from the fact that the rear upper A-arm isn't mounted parallel to the vehicle, but angled backward (image), so the lift causes the axle hub to lean forward into the control arm which therefore turns the wheel outward.

• Before the lift, the rear wheels did have clearly visible negative camber, and the car was running dead straight, and turns were "on rails".
• Now with the lift kit, that camber is practically zero, and the rear wheels are visibly toe-out and when you now drive the car, it's obvious that the rear axle doesn't want to go straight; taking a turn feels like the rear wheels are actively steering opposite of the front wheels. Very effecitve for turning, but not what it's supposed bo be :)

In the front, it's not a problem because both toe and camber were fine before and after. Front upper and lower A-arms are mounted parallel to the vehicle (image).