You won’t. It’s not a configuration item, but a term used by many users to describe operation with the lid closed (via an external monitor, keyboard and pointing device).
Since you have an external display, does it go black when you close the lid? What about if you click the mouse with the lid closed? If the Mac wakes up (making your external screen your only display), then that is “clamshell” mode. And it explains why everything is moving, since this is causing it to change from a dual-display desktop to a single-display (external only).