MacBook Pro won't sleep when the lid is shut.
I have a MacBook Pro with an external monitor connected via HDMI. I use the external monitor as a 2nd screen and I leave it on and plugged in constantly. Right now when I shut the lid to my MacBook Pro, rather than the whole machine going to sleep, my main display is switched over to the external monitor. I realize that this can be useful in some applications, but for my purposes I want the whole computer to go to sleep when I shut the lid, while leaving the external monitor plugged in.
MacBook Pro 13", macOS 10.15