How to protect bike frame mounted on the carrying rack?
Pool noodles, cut lengthwise and held in place with gaffer tape (or hockey tape if you're so-inclined)

Bonus marks for colour-coordinating with your bike and car.   Do the whole length of the rack upstand, not just the contact point.



Like this but on the upstand too, not just the tines.



You could put the protection on the bike, like this, but its more likely to fall off.  Velcro cable ties can help here.