My laptop screen isn't working, But I have an external monitor. Is there a shortcut to move from one to the other?

Normally, an external display is automatically detected and enabled in extended or mirrored mode (depending on what is selected in System Preferences > Displays > Arrangements. You might try clamshell mode, where you use an external display with the lid closed, also requires an external keyboard and mouse/trackpad, and connecting to AC power.

Comand-BrightnessDown will toggle the setting of [√] Mirror Displays.

If you don't have desktop wallpaper on the external display yet, you still have a long way to go.

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