Good HiDPI scaling on my external Monitor is one of the reasons i switched back to os x. For me that works very good independent of the monitor manufacturer.
Any notebook with Windows and multiple Linux distros work with HiDPI scaling on any combination of my various docks, monitors, and cables.
Apple definitely does not "just work" in this case. They really "think different" as in different standards to ensure consumer lock-in in their walled garden.
IME, macOS handles mixed HiDPI better than any other OS. I'm currently using a MBP with it's HiDPI screen and it's driving an LG 4k and a Dell 1920x1200 - all work and look fine.
I've tried Linux a few times in the past and it's been a mess - particularly in a mixed DPI environment. It also seems to come down to individual apps rather than the desktop manager. Not long ago I really wanted to make linux worked and so was asking questions on forums on how to make HiDPI work well, and a common response was 'no one needs HiDPI'...got it.
Apple definitely does not "just work" in this case. They really "think different" as in different standards to ensure consumer lock-in in their walled garden.