WindowsOn Windows, you can use the keyboard shortcut (Windows Key + P) to bring up the display picker that gives you the option to select one of the following display modes:
Computer/PC screen only - The second screen is ignored and only the PC’s primary display is used.
Duplicate - The second screen mirrors the primary display.
Extend - The PC display is extended across all screens.
Projector/Second screen only - The main PC display will be disabled and only the secondary screen is used.
Below are screenshots of what the display picker looks like on Windows 7 and Windows 10.