macOS Sequoia Not Detecting Second Display? Fix

You can connect more than one monitor on your Mac. If your Mac suddenly stopped detecting your external monitor after updating to macOS Sequoia, you’re far from the only one. A growing number of users across different Mac models—including MacBook Pro, iMac, and Mac mini—have been hit with the same frustrating issue.

What’s the Problem?

The issue typically shows up right after installing the macOS update. For many, their second display—especially connected via Thunderbolt or HDMI—just goes dark. It doesn’t show up in display settings, and clicking “Detect Displays” (even while holding Option) doesn’t help. Some users reported that their monitors go into power-saving mode, while others said the Mac does detect something, but nothing appears onscreen.

Even worse, some users tried using known-good cables and monitors that still work fine on macOS 15 or other machines, only to hit the same wall with Sequoia.

Note: We’ve previously covered how to set up and use a second monitor with your Mac.

Fixes That Worked for Some Users

Here are the solutions that actually helped some people get their second monitor working again. These aren’t guaranteed, but they’re worth trying:

1. Delete the WindowServer Display Preferences File

Many users had success deleting the system preference file related via the Library folder to display configuration.

Steps:

1. Open Finder, click Go > Go to Folder, and enter:

   ~/Library/Preferences/ByHost/

2. Look for a file that starts with:

   com.apple.windowserver.displays

It may have a long string of letters and numbers in the name, ending in .plist like below:

Note: If you’re wondering what a .plist file is, we explained that in a separate article — feel free to check it out on our site.

3. Move that file to the Trash (or just drag it to your Desktop to be safe).
4. Then go to:

   /Library/Preferences/

and delete this file (you’ll need admin rights):

   com.apple.windowserver.displays.plist

5. Restart your Mac. After reboot, replug your display to see if now it is working.

2. Flip the Thunderbolt/USB-C Cable Around

Some users said that simply unplugging their USB-C or Thunderbolt cable and flipping it—plugging the end that was in the Mac into the monitor and vice versa—magically fixed it.

3. Use the Display Menu App

One user mentioned that while macOS couldn’t detect their monitor through System Settings, a free App Store utility called Display Menu could. After installing it, the app was able to recognize the monitor and allow the user to extend or mirror their display.

4. Drop the Refresh Rate

In some cases, dropping the refresh rate from 75Hz to 60Hz made the monitor come to life—especially with 4K displays. Go to System Settings > Displays, and see if you can manually change the refresh rate.

5. Unplug Everything and Wait

Another method that worked for some: unplug all cables from both the Mac and monitor, wait five minutes, then reconnect and boot up. Some described this as a “hardware handshake reset” that somehow jolted the monitor back into recognition.

Still Not Fixed?

If you’re affected, you should definitely submit feedback to Apple. It’s the best way to get their attention and (hopefully) push for a fix in the next update.

You can submit feedback here: https://www.apple.com/feedback/