I’m mainly worried about damaging the joist that runs along the top of the lower wall. If I drill up from the receptacle cutout with the flex auger it will maybe go behind the joist but if they are doubled it will just go through one, probably at a weird angle.

The upper wall puzzles me a bit because it is offset and seemingly just sitting on the plywood then air, but I’ve been looking for the endoscope I could have sworn I accidentally stole from work to get a better idea of whats going on. I might just take down more drywall if I can’t find it.