The new iPad Pro 12.9" with M1 processor has a mini-LED display with 2,500 local dimming zones providing 1,000,000:1 contrast ratio. 1,000 nit peak brightness overall, and 1,600 nit peak brightness for small areas of the screen in HDR mode.
Although its not 4K, 2388x1668 in a 12.9 inch screen might be good enough, particularly with 120Hz refresh rates. Might be the closet affordable thing to a reference display for watching HDR10 and Dolby Vision content