for 1920x1200 HiDPI, you need to add a scaled resolution of 3840x2400. On an Intel Mac, I would use SwitchResX to do that. I don't know if anyone has been able to add a scaled resolution to an M1 Mac using SwitchResX. I believe people were able to at least change the display name - which is in the same override file where the custom scaled resolutions are stored.