Mac Not Detecting External Monitor? Fix for Samsung Odyssey G9 (DisplayPort 1.4)

If your Mac suddenly stops detecting your Samsung Odyssey G9, especially when using DisplayPort 1.4 or USB-C, you’re not alone.

This issue commonly appears on M1, M2, and M3 Macs and can be extremely confusing because everything looks like it should work.

Typical symptoms include:

The Mac screen briefly flashes when you plug the monitor in
The monitor stays black or shows No Signal
The monitor does not appear in macOS Display Settings
HDMI works but DisplayPort does not
DisplayPort 1.1 works but DisplayPort 1.4 fails

After hours of troubleshooting cables, firmware, and monitor settings, the real cause turned out to be something unexpected:

Corrupted macOS display configuration files.

Luckily, fixing it only takes a few minutes.

The Real Fix: Reset macOS Display Configuration

macOS stores external display information in system configuration files. These files store things like:

Monitor EDID information
DisplayPort configuration
Resolution and refresh rate settings
Display Stream Compression (DSC) capabilities

If these files become corrupted, macOS may detect that a monitor was plugged in but fail to initialize it correctly.

Deleting them forces macOS to rebuild the display configuration from scratch.

⚠️ Warning: This resets display settings. Your Mac will rebuild them automatically after reboot.

Step-by-Step Fix

Tested on:

MacBook Pro M3 Pro
Samsung Odyssey G9 OLED
macOS Tahoe 26

1. Disconnect the Monitor

Unplug the monitor completely from your Mac.

2. Open Terminal

Go to:

Finder → Applications → Utilities → Terminal

3. Run These Commands

Run these commands one at a time:

rm -f ~/Library/Preferences/ByHost/com.apple.windowserver.displays*.plist

sudo rm -f /Library/Preferences/com.apple.windowserver*.plist

sudo killall Dock

You will be prompted for your administrator password.

4. Restart Your Mac

Restart normally from the Apple menu.

 → Restart

5. Reconnect the Monitor

Once the Mac has rebooted, reconnect your monitor.

The display should now appear in:

System Settings → Displays

Why This Works

macOS caches monitor configuration data in hidden .plist files.

If those files become corrupted, macOS may attempt to use invalid display configuration data when negotiating the DisplayPort connection.

Deleting the files forces macOS to:

Re-read the monitor’s EDID
Renegotiate DisplayPort capabilities
Rebuild the display configuration database

This resolves many cases where external monitors are detected but fail to initialize.

Additional Tips for Samsung Odyssey G9 Users

If you’re using a Samsung Odyssey G9, also check these monitor settings:

Menu → Game → Adaptive Sync → OFF

Menu → System → DisplayPort Version → 1.4

macOS tends to behave more reliably when Adaptive Sync is disabled.

Final Thoughts

If your Mac suddenly stops detecting an external monitor, the issue may not be your cable, dock, or monitor hardware.

Sometimes the problem is simply corrupted macOS display configuration files, and resetting them can restore normal operation in minutes.

This fix resolved my Samsung Odyssey G9 DisplayPort issue instantly after hours of troubleshooting.

This fix originally came from a Reddit discussion where several users experienced the same issue with Macs not detecting external monitors.

View the original Reddit discussion

You can find more fixes in our Troubleshooting section.