If you close one eye, it’s clear that each of your eyes sees a side of your nose, but if you open both, the nose sort-of disappears from your perception (you can still see it, but have to cross your eyes to do so)
Your brain somehow creates a unified geometry from those two views (and manages to keep that around if you move your eyes)
And it’s weirder: your brain/body also knows how the various angles of the joints in your arms and legs combine to move your arm to things you see, or to direct your gaze to parts of your body (try directing your gaze at your index finger with your eyes closed. That’s fairly easy, but the goniometrisch isn’t).
Also, the world isn’t flat, so why would pictures and movies be flat?
Given that, I don’t think making picture frames rectangular because that’s easier makes a difference.