I came here to figure out why my wife's iPhone 12 does not unlock here car, while my iPhone 11 does.
Someone mentioned back pocket vs front. I gave it a try and sure enough, if I put my phone in my back pocket, it does not unlock for me either. Then I had her try her front pocket, and it works fine.
Not ideal, since many of her pants don't have big enough pockets for a phone, but at least now she can unlock the car without getting her phone out by turning around.