you get what you pay for, and it's usually in the black level.
The expensive ones are typically OLED, on those each individual pixel lights up. So for a black part of the image, no pixels are on, meaning you get really dark blacks.
the others are typically LED, or QLED. On those, there is a white backlight behind the entire screen, it goes through a color filter (bunch of tiny red, green and blue squares, one for each pixel) and the image is produced by tiny LCD shutters either blocking the light or allowing it to pass. It typically doesn't block all the light, so your blacks are more grey. Depending on the price, you might get a zoned backlight where it can turn down the backlight in certain portions of the image. This will help with the darker parts of the image, but can also lead to halos around bright parts of the image since dark parts of the image bordering bright parts share backlight zones. Again price is key here, cheaper sets might have one backlight (less common now) more expensive might have what's called microLED backlights, with 1000 or more zones. QLED works exactly the same as LED, except its RGB filter is done using quantum dots, which allow for a much more precise color. QLED also allows for a bit brighter image compared to LED
pricer units also typically have faster electronics. Which will lead to faster input switching, and potentially a better gaming experience. Also when switching input types (frame rate, SDR to HDR) most TVs black out for a moment while it re-syncs to the new signal. On cheaper models, that might be out for 2-3 seconds, on more expensive closer to 1, and on some of the newer ones, they've made a way so that it doesn't black out at all.
Matching the frame rate to the video that is being played will cause smoother motion.
Dynamic range allows for more colors and a brighter image. YOu'll typically see SDR (standard dynamic range), HDR (High DR), or Dolbyvision. In a SDR image, each color (R,G,B) of each pixel can be one of 256 steps (0 thru 255), allowing for about 16 million total combinations, In an HDR image, each color has 1024 steps for just over 1 billion combinations. Best way to visualize this is underwater scenes, on cableTV where it's compressed even more than SDR, you'll typically see bands of colors. IN HDR you have more colors available, so the it can smooth out those bands more. Also HDR is brighter. To vastly simplify, SDR has 256 steps from 0 to 10 brightness, HDR has 1024 steps from 0-15 brightness. so more steps over a bigger area.
AppleTV allows you to match both frame rate and dynamic range.
wiki article explaining why you should match frame rate -
https://en.wikipedia.org/wiki/Three-two_pull_down
Differences in HDR and SDR -
https://www.rtings.com/tv/learn/hdr-vs-sdr
backlight explinations -
https://www.cnet.com/tech/home-ente...how-it-improves-samsung-tcl-hisense-roku-tvs/
