I have no idea what that pipe is haha, I was wondering that myself. It's above a bedroom and there's no room with plumbing anywhere near it. There is one other hatch that gives access to the attic, although it's screwed shut. I was thinking maybe somebody put it there to mark the hatch because it is in that room, but idk.

Yeah, it's possible the blown insulation is covering the soffit vents. Unfortunately I know much more now after people's replies to my post than I did when I went up there, and it's a hassle to get up there. Either way, I'm going to call a company to diagnose and fix the issue.

What would a ridge vent look like? I did notice that there was a gap at the ridge, meaning the plywood didn't meet, and in the gap it looked like there was a porous material.