l know you have to buy a license plate bracket to hold on the front plate. Supposedly there are two dimples where you screw in the two mounting screws.What do the screws actually screw into, is it just the rubber bumper cover or do they go into any metal?
l find that a bit confusing.l have strong magnets and neither of them are able to find any metal in the area.

They actually go into a metal bracket located within the bumper cover.

Aluminum is a type of metal and is non-magnetic. Unless you have an aluminum magnet? If you do l want one. ;-)

l do not think there is much metal underneath those bumpers. l had the rear bumper replaced a few years ago and it is mostly plastic. After l had my new bumper installed my son managed to poke a hole clear through it with the reflector on his bicycle so l know there was no metal there.

l do not know if this helps you or not.