How to Truly Full-Screen Window in macOS Stage Manager (Even with an External Keyboard!)

macOS users often struggle with the Fill shortcut (Fn + Control + F) when using an external keyboard in Stage Manager mode. This shortcut is meant to fill the screen with a window, but it doesn’t always work as intended with third-party keyboards. The issue lies in how macOS interprets the keyboard’s Fn key – it doesn’t recognize the combination as a Fill command when using external keyboards directly. However, there is a simple solution to ensure that the Fill shortcut works seamlessly on any keyboard setup.

Firstly, it’s essential to understand the difference between Full Screen and Fill modes. Full Screen mode moves the active app to a separate screen space, hiding Stage Manager and other apps entirely. On the other hand, Fill mode stretches the window edge-to-edge on the current desktop, keeping Stage Manager active and the automatic hide function intact. The latter is usually the preferred option for users who wish to maximize their screen space without isolating the app into its own virtual monitor.

The reason why Fn + Control + F doesn’t work with external keyboards is that the Fn key is processed internally by the keyboard for hardware controls, and macOS only recognizes the Control + F combination, which is not the Fill command. To remedy this, users can create a custom shortcut for the Fill command using built-in macOS settings.

First, open System Settings by clicking the Apple logo in the top-left corner of the screen and selecting System Settings. From there, navigate to Keyboard and click on the Keyboard Shortcuts… button. In the new window, select App Shortcuts on the left, and then click the + button at the bottom to create a new shortcut. Assign the "Fill" command to a standard modifier key combination like Control + Option + F. This ensures that the shortcut works even on external keyboards.

Lastly, for users who prefer using third-party apps like Rectangle for window management, you can configure the app to stretch windows to the full screen width without reserving space for Stage Manager. Quit Rectangle from the menu bar, open Terminal, paste the command "defaults write com.knollsoft.Rectangle stageSize -float 0," and press Enter. Reopen Rectangle, and it will automatically stretch windows across the entire screen width.

By following these steps, macOS users with external keyboards can easily enjoy the benefits of the Fill shortcut, ensuring a more efficient and clutter-free workspace.