To quit (close) a Mac app normally, choose Quit from the app's menu in the menu bar, or press Command (⌘)-Q. If the app doesn't quit, follow these steps to force the app to quit.

How to force an app to quit

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Press these three keys together: Option, Command, and Esc (Escape). Or choose Force Quit from the Apple menu  in the upper-left corner of your screen. (This is similar to pressing Control-Alt-Delete on a PC.)

Force Quit A Program On Mac

Then select the app in the Force Quit window and click Force Quit.

You can even force the Finder to quit, if it stops responding: Select Finder in the Force Quit window, then click Relaunch.

Learn more

Quit All Apps Mac

How to force an app to close on your iPhone, iPad, or iPod touch.