I recommend you save a single frame from several versions of a film (VLC: Shift+S) and flip through them quickly in an image viewer that instantly jumps to the next image (Eye of GNOME) to see the differences. I’ve found surprising differences in cropping, aspect ratio, brightness, and color tone - some people are just incompetent at encoding. With good but heavy compression, only the finest details are blurred - especially film grain disappears when file size goes down from huge to big. That’s actually a plus sometimes when there’s so much grain I start itching and thinking of an ants’ nest. My Sony phone records UHD @ 120fps in h.265, 60GB/hour. I’ve never seen a BluRay remux take that much space, but surely they exist.