This utility turns off the MacBook display when it connects to an external monitor

Add it to the list of trivial things macOS inexplicably can’t do: turn off the laptop display when it connects to an external monitor. Until yesterday, what I did was use a utility — MonitorControl — to reduce the built-in display brightness to the minimum. It’s effectively off, but still active, meaning the mouse “wanders off” into the darkness and, depending on how the monitors are arranged, the Dock ends up hidden on the blacked-out display. I happened to come across a tiny free app by Jeremy Kanter, suggestively named One Display, that turns off (really turns off) the built-in display as soon as the laptop is connected to an external screen. To my surprise, it works! There are only two options in One Display: Launch at login (Start at login). A keyboard shortcut to toggle the laptop display on and off. The default is Control + Command + B. In an ideal world (or operating system), this functionality would be native. I know the KDE Plasma graphical environment does this. In macOS,…