On Windows, press Ctrl + Shift + Esc to open Task Manager
Select the application
Click End task
On Windows, press Alt + F4 to close the active window
If it does not respond, use Task Manager
On Mac, press Command + Option + Esc to open Force Quit Applications
Select the application
Click Force Quit
On Android, open Recent Apps
Swipe the app away
If needed, go to Settings > Apps > [App] > Force stop
On iPhone, open the app switcher
Swipe the app up to close it
On Linux, open System Monitor or Task Manager
Select the application
Click End Process or Kill
On Linux terminal, use kill or kill -9 with the process ID