from what i can gather all wings, spoilers ( especially oem ones) will cause a little downforce unless they just a big flat airbrake ie bugatti, p1. .
spoilers are named as such that they spoil the airflow on the back egde of the car thus creating negative air pressure behind the car mean the weight of the car and air pressure over it push the car lower at the rear as less resistance.
big wings on the other hand put high enough (about same hight as roof maybe little lower) and they have a larger surface area result in the airflow over the roof taking an easier root over this surface than continuing down the boot as this air has less resistance ie no curve down the bootline it travels faster than the boot airflow and thus creates actual downforce on the rear of the car .
both result in drag
but benefit of drag vs downforce is decided as more rear grip mean power on the ground for a little more aero resistance