How to exit from stuck full screen application on Windows 10?

The usual way to get into and out of full screen mode is by using the F11 key.

If this does not work for you, try to hit Alt+Space to open the application menu and click (or use the keyboard) to choose Restore or Minimize.

Another way is to hit Ctrl+Shift+Esc to open the Task Manager. If it is still covered by the always-on-top full-screen program, press Alt+O to open its Options menu and then Enter to select Always on Top for the Task Manager.