Some DOS games do not respect the mouse cursor position, they take into account only relative movement of the mouse cursor. This type of game requires a mouse locking feature.
When the mouse is locked DOS game recive only relative movement of mouse and cursor can't leave game screen. This often used inf FPS games like DOOM to look around.
Mouse lock feature is incompatible with mobile devices. Changing the
autolock property does not have any effect on mobiles.
To activate mouse locking just enable the
autolock property in dosbox config. Mouse will be locked automatically when you click on the game screen.