There a couple of catches... one of them pretty severe, but a new 4:3 HDR OLED monitor exists.
I have one, and a mister -> Retrotink 4k setup produces a fantastic result with it.
The resolution is 2560x1920, which isn't quite 4k level (that would be 2880x2160), but at 17.3" it's enough pixels for a very good CRT filter.
Unfortunately, it costs a fortune: $2199. An absolutely silly amount for a 17" portable monitor. The reason is obviously because of the other catch: It's a folding screen. But hey, the fact that it's a folding screen is probably the only reason someone bothered to make a decent 4:3 OLED monitor.
ASUS ZenScreen Fold MQ17QH
https://www.asus.com/us/displays-deskto ... ed-mq17qh/
Like many folding screens, it doesn't quite reach 180 degrees. Maybe 179. As a result, a small fold is visible and you can see it in my photos, but it's actually substantially less obvious in person.
I measured the added input latency at less than a frame, but I lack the tools to get extremely precise. I estimate very roughly 8ms combined from the Retrotink and monitor.
The monitor will sync to a 55hz signal from arcade games like R-Type, or an x68000. It will not sync to a 61.5hz signal. When it works, I have no sync problems and scrolling is smooth in everything I tried. I can use the Retrotink 4k's gen lock and frame lock modes without a problem.