I have successfully managed to inject a 1920x1200 resolution into the Macbook Air M1 running Big Sur 11.3 Beta 3.
OS: macOS Big Sur 11.3 Beta (20E5196f)
Tool: SwitchResX Beta 4.11.1a4 (Build 2022)
Method:
Comments: Resolution works well and without issue. At present, I am unaware of how to accomplish this without an app, but SwitchResX is extremely light and effective.
- Install SwitchResX Beta.
- Open SwitchResX within System Preferences.
- Navigate to About SwitchResX
- Install Helper tools and Launch Daemon.
- Select Internal Display on the left-hand menu.
- Select Custom Resolutions
- Click the + icon at the bottom left-hand side.
- Ensure the options dropdown on the top left-hand side is Scaled resolution
- Enter 3840 under Horizontal Resolution
- Enter 2400 under Vertical Resolution.
- Click OK
- On the System menu for SwitchResX on the top left hand of the entire screen click Display.
- Click Write System Settings
- Reboot your machine.
- Navigate back to SwitchResX upon reboot
- Under the Current Resolutions tab, look for a new HiDPI resolution of 1920 x 1200. 60 Hz.
- Activate by clicking the radio button to the left of the resolution.
Tried without success it shows 'Not active' and there is no way (I tried to reboot)
Very very disappointed with Apple.