Looks like somebody pushed on the spoiler. It happens when the uninitiated use it as a method of pushing the car to bump start it. The crack looks fresh as if it just happened. The red paint on the fracture looks like where the fracture scraped the other part as they separated.
You may be able to use some fiberglass resin and hardener to bond it back together. If you can remove the screws that hold the stand onto the wing, I have the well nuts that are needed to reattach the stand. I found that I had to insert a putty knife between the wing and stand and exert just enough pressure to keep the well nut insert from spinning in the wing cavity.
Using the catalyzed resin, put a piece of non-stick foil between the wing and stand, apply the catalyzed resin, reattach the two pieces to the wing and put some weight on the stand to hold it in place until it cures. The foil is to keep it from bonding to the wing.
In the meantime, get some of the umbrella push plugs and put into the deck lid to keep the water out of the trunk. You can get different sizes at the parts store, with a smooth rounded head and just push them down into the stud holes.
If the fiberglass resin doesn't work, next would be to secure another stand. Difficult and maybe expensive to find. Looks like the left side? I'll check the stand I have in the shed, but it's black so would need painted.
