What about 4096?

4K = 2160P

Pretty sure it's like 4°K = -269.15°C

It is indeed just Kelvin, not degrees Kelvin.

3840 x 2160

But Celsius are still °C

I thought Kelvins were measured in radians not degrees?

Nope, Kelvins are a countable unit, like meters. Celsius and Fahrenheit are not.

A bit like 2000 requires “year” 2000

Depends.

https://en.wikipedia.org/wiki/4K_resolution

Is the difference that they can go negative or...? I never quite understood what makes them "degrees"

Both main standards have the same vertical resolution. Cropped versions hardly count as "standard"

No, the difference is that if you double a kelvin number, you have quantifiably doubled the heat. If you double a Celsius or Fahrenheit number, you have not quantifiably doubled the heat… the number does not objectively count an amount of something.

Think meters. A meter measures an exact length. Two meters is double one meter.

Celsius doesn’t do that. Celsius is a scale between two amounts of heat.

The equivalent for distance would be if we had a scale where 0 degrees distance was equal to 582.7762 meters, and 100 degrees distance was equal to 721.5323 meters. Each degree between 0 and a hundred is then a slice of that range. Maybe for the people who designed such a scale there’s useful reasons to do so, but you aren’t measuring the quantity or amount of something, you’re measuring a range.

Kelvin measures molecular movement, just as hertz measures oscillations or cycles, or grams measure weight.