Press and hold Option + Command + Esc
Select the app you want to quit
Click Force Quit
If the app won’t respond, press Command + Option + Esc to bring up the Force Quit window again and select the app
Restart the Mac if needed: click the Apple menu, then Restart
If the Mac won’t restart normally, force power off: press and hold the Power button until the Mac turns off, then press Power to turn it back on