Waist-level finders or viewfinders aren’t completely non-existent on modern digital cameras. There’s the cheap toy camera Chuzhao.On the other end of the spectrum, the Hasselblad CFV 100C ...

I used to have a 35mm Kyocera Yashica T5 with a waist-level viewfinder. It was basically just a thumbnail-sized curved mirror matching the camera’s (fixed) FoV, but it worked surprisingly well.