I have it attached by a few of the screws, not all of them. If I recall, there are some SS screws and plastic ones that lock/unlock. I have some lead bags back there and a few skim boards. The area is not that big, so once that stuff gets in there, that plastic cover would not move even if the screws came out.
I think the new models have a fancier cover that protects the back of the motor.
2018 Supra SL400