Press Command + Option + Esc
Select the app
Click Force Quit
Click Force Quit again if prompted
Use the Apple menu
Click Force Quit
Select the app
Click Force Quit
Open Activity Monitor
Find the app
Select it
Click the Stop button
Choose Force Quit
Right-click the app in the Dock
Hold Option
Click Force Quit
Use Terminal
Run `killall AppName`
Run `pkill AppName`
Use `sudo kill -9 PID` if needed