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
Messenger For Mac
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.)
Then select the app in the Force Quit window and click Force Quit.
Connect with friends, family and people who share the same interests as you. Communicate privately, watch your favourite content, buy and sell items or just spend time with your community. On Facebook, keeping up with the people who matter most is easy. Discover, enjoy and do more together. Facebook is an average social media app that is nice for communicating with friends and family for free (via Messenger). But, with that being said, it is time for Facebook to release a major design update for the mobile app. Often, when I am checking the reactions to my posts on Facebook, the reactions never load, are miscounted, or not updated.
You can even force the Finder to quit, if it stops responding: Select Finder in the Force Quit window, then click Relaunch.
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How to force an app to close on your iPhone, iPad, or iPod touch.