Magnetic car mounts for iPhone
ANSWER - I currently use an iPhone 12mini with an Apple leather case. I have a round metal disc about 2 inch diameter inside the case at the bottom (not attached to phone or case). Because it is small enough to be below the sweet spot for the MagSafe, the phone still charges when placed on the MagSafe charger.
The metal disc provides enough hold power on my magnetic car mount to be usable. If it was stuck with adhesive to the case or phone, it might provide a more stable mount for larger phones.
iPhone 12