> I'm assuming displays have detectable ids of some sort?

Yes, the EDID information uniquely identifies a screen. https://en.m.wikipedia.org/wiki/Extended_Display_Identificat...

> Why can't linux do this?

It does for me (fedora, gnome, wayland). Other stacks are more work. I was put off using Sway as my desktop, because screen resolutions and layouts was manual.

It gets better. One of my ASUS monitors has a defect (it kicked in after several years of use) where it no longer provides EDID information. I believe that on windows and macOS this would effectively be the end-of-life for the monitor, which is a shame since in every other way it is still 100% functional. On Linux, I was able to tell the kernel to use a file for the EDID information, and created the file using the other (identical) monitor.

Very much a corner case, but also another perfectly good monitor kept out of a landfill.

Windows may actually let you override the EDID info, it's been a while since I used windows but I think it lets you do it in device manager... from the era when displays came with drivers on a cdrom.

There are also EDID cloner/emulator hardware solutions that you plug in inline on the display cable.

Kanshi is the default solution when you need dynamic monitor management in Sway: https://sr.ht/~emersion/kanshi/

My linux machine remembers the displays and where I place them relative to each other (I'm not using a laptop).

But ... I sometimes use 1, 2 or 3 of the displays, and the configuration needs to be different depending on the number and specific displays in use.

My Linux machine can do this automatically, because this is scripted. Maybe you can do this on macOS also, but I doubt it can be done with nothing but the GUI tools.

macOS does do this without scripts. It remembers combinations of attached monitors and where I want them, absolutely.

ime, this isn't totally accurate in the world of usb-c HDMI dongles. I've had the same 2 monitors plugged into the same 2 ports since the machine went to sleep, and it will occasionally switch their positions upon waking.