The Multi-Monitor Menu Bar Issue
By default, when you connect an external monitor to your Mac, macOS treats each display as a completely independent workspace. This feature, known as “Displays have separate Spaces,” means that each monitor gets its own menu bar at the top, and if you make an application full-screen on one monitor, the other monitor remains usable and independent.
However, this independent behavior breaks one very specific workflow: spanning a single application window across multiple monitors. If you try to drag a large spreadsheet or a video editing timeline so that half is on your MacBook screen and half is on your external monitor, the window will simply disappear at the seam. It cannot cross the boundary because the screens are treated as separate “Spaces.” If you need to stretch windows across screens, you must disable this feature.
How to Disable Separate Spaces for Displays
You can change this behavior in the Desktop & Dock settings, but it requires a logout to take effect.
- Click the Apple Logo in the top-left corner of the menu bar and select System Settings… (or System Preferences).
- Scroll down the left-hand sidebar and click on Desktop & Dock (or click “Mission Control” if you are on an older version of macOS).
- Scroll down the right-hand pane to find the Mission Control section at the very bottom.
- Look for the toggle switch labelled Displays have separate Spaces.
- Toggle the switch to the Off position (or uncheck the box).
- A small warning dialog will appear, informing you that you must log out for the changes to take effect.
- Click the Log Out button on the dialog box (ensure you have saved all your work first).
When you log back into your Mac, your monitors will act as one giant, continuous canvas. You will only have one menu bar (on your primary display), and you can freely drag a single window so that it spans across the physical gap between your monitors.