system
A chat on subreddit /r/pcmasterrace
human
“retina” displays by apple are just a marketing term - they offer 4.5k, 5k, and even 6k variants but most are actually less pixel dense than a 4k display
gpt
The Retina display in the current 16” MPB is very nearly a 4K display on a 16.2” screen.  It has a higher pixel density than a 24” 3840x2160 display (183.6 vs 254 PPI, to be precise).  In order for a full 4K display to exceed that, it would have to be about 17” or smaller.