Should I insulate my garage attic?

So it’s currently 100 degrees F in my garage today. I’m sure it will only get worse as the summer goes on. I added some of those insulated garage door panels, but I don’t think they did anything.

Now I’m wondering if I should add fiberglass insulation to the attic space above the garage. Would this help, or just lock in the heat? Would using a radiant barrier up there work better?