Sometimes when I use an external display with my MacBook Pro in clamshell mode, nothing shows up — I just get a black screen. And when this happens, forcing macOS to “Detect Displays” can help.
To trigger “Detect Displays” on macOS, just hit Command+F2 (brightness up).
You can also do this using the trackpad:
- Navigate to System Preferences > Displays
- Hold down the Option key to reveal the Detect Displays button
- Click Detect Displays
This works in macOS Mojave, and others have reported it works with previous versions of macOS.
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