Engine Display Window

In Reality Hub terminology, Engine Display Window refers to the separate scene-preview window that activated on the Engine Host.

Launch Parameters

To utilize it, you have to disable renderoffscreen option in the Launch Parameter section, as illustrated above.

This window is sometimes called the Game Preview Standalone or the Render Preview Output.

Image courtesy of Virtual Line Studios & ASK Co.
Unreal Engine Display Window

To disable the full screen, click F11 on your keyboard.

Instead of going back and forth to the Engine Display Window to check your scene, you can utilize the Advanced Preview Monitor feature without leaving the Reality Hub interface.