Which key can be used to temporarily hide all open windows and bring the desktop in focus?

The key combination that allows you to temporarily hide all open windows and bring the desktop into focus is Command-M. When you press Command-M, it minimizes the active window, which helps you clear your workspace by pushing the window out of view. While it may not directly show the desktop in the same manner as other shortcuts, it does allow for a cleaner workspace by minimizing windows to the Dock.

To bring all windows into focus—and not minimize them—you would typically use F3 or Mission Control which allows for different workspace management but does not directly ensure the desktop becomes the primary focus through minimizing. Command-D is used to duplicate files or windows, while Option-D toggles the Dock's visibility, but neither serves the purpose of hiding windows to focus on the desktop like Command-M does. Understanding this function is key for efficient navigation and management of multiple applications on a Mac.