The screen technology is the biggest differentiator. Cheap sets use LCD. Some will have local dimming zones where parts of the backlight dim in order to increase contrast a bit, but there is light bleed which I find distracting

There’s a newer tech called mini LED which is basically an LCD with an array of much smaller led backlights behind it than a cheaper set. This allows for much more precise local dimming of pixels, creating a picture with a better contrast ratio and much less light bleed.

The more expensive stuff is OLED which is a different technology entirely. Its main benefit is that each pixel is lit independently without the need for backlighting which provides VERY deep blacks (the pixels are off), often described as a near infinite contrast ratio, with no light bleed. The main drawbacks are low peak brightness and the possibility of burn in, though both are getting better with time.

The newest and priciest is micro LED, which uses self illuminating LEDs as pixels so it has the same contrast advantages as OLED but it has much higher peak brightness and no burn in. This is extremely expensive and not widely available yet, but is being pitched as replacing OLED eventually.