macOS is a pain as well. There was a fairly well documented way (in the open source world) of writing a stub driver to create a virtual display. Apple axed it without notifying anyone when their own "Use an iPad as a second screen" support came out. All the third party apps that provided that function broke overnight, notably Duet Display.

Considering Duet works again, I wonder if the mechanism they use was quietly shared with them or if it was publicly shared.