In #12 of the P4 FAQs in the DJI website they state the camera and gimbal are made of composite material, whatever that means.Touching it you can't really tell if it's plastic or powder-coated aluminum. Might be able to tell removing the camera back & flexing it but I don't really want to take it apart.
I know the camera, gimbal components, & gimbal base plate were all aluminum on the Vision+. V+ gimbal parts usually bent in a crash. I suspect the P3 cameras & gimbal may be plastic...especially the base plate...due to how many I see broken in two.
"The gimbal and camera system is integrated into the body, bringing it closer to the aircraft’s center of gravity. It is also made of a rigid and strong composite material"