Can't turn off iTunes on MacBookAir I cannot quit from iTunes, possibly because there is a pop-up that will not cancel, despite dozens of times pressing the cancel button.  I turned off the machine and when I turned it back on, there was iTunes and the stubborn pop-up.  I'm using MacBookAir, bought in December 2019.
There can be multiple things happening here. If you have the spinny wheel, iTunes is obviously hanging/not responding. You can fully quit it by using Option + Command + Escape, selecting iTunes, and pressing Force Quit. If that doesn't work, you can open Activity Monitor (You can press Command + Space and then type Activity Monitor), find and select iTunes, and press the Stop symbol with an X in the center, and that should be the end of that. If none of this works, you can restart.