MacOS – Menu bar turns red on secondary screen

Try this:

• Go into Displays Preferences > Check Mark the box for "Show displays in menu bar"

• Under the resulting icon in the menu bar, drop the menu and set "Number of recent items" to 10.

• Click the menu again and you should see a list of recently used timings/formats. Multiple 1920 x 1080 might appear, switch to one or the other and it might just fix your issue.

Also:

In Displays Preferences > Displays > “Options” tab/button near the top of the window and make sure the “overscan” box is checked.

It would be helpful to know if you're trying to run 1080i or 1080p, and what model of your external display is.

You might try force quitting Dock with killall Dock. It should be reopened automatically by launchd. The Dock process seems to be responsible for many general UI features like Mission Control and the application switcher.

You can usually just log out and back in instead of restarting the OS. sudo killall loginwindow would be even faster than that, but it only seems to quit some processes.