User profile for user: Abrar_95
Abrar_95 Author
User level: Level 1
4 points

MacBook Pro M4: Only one external display detected

I’m having a strange external display issue on my MacBook Pro M4.

Setup:

  • MacBook Pro M4
  • Two external monitors
  • One connected via HDMI
  • One connected via USB-C to HDMI

The setup was working perfectly earlier the same day. After shutting down the Mac and turning it back on later, macOS now only detects ONE external monitor at a time.

Current behavior:

  • If I connect Monitor A first, it works.
  • When I connect Monitor B, Monitor A immediately disappears from macOS Display Settings.
  • If I disconnect Monitor A, then Monitor B starts working.
  • Whichever monitor is connected last becomes the active external display.
  • macOS never detects both simultaneously anymore.
  • Sometimes the inactive monitor shows wallpaper/background briefly but is not actually detected in Display Settings or System Report.

What I already tested:

  • Both monitors work perfectly together on a Windows laptop
  • Both monitors work individually on the Mac
  • Both Mac ports work individually
  • Different cables tested
  • New USB-C to HDMI cable tested
  • Safe Mode tested
  • Different macOS user account tested
  • Apple Diagnostics passed with no issues found
  • Reinstalled macOS completely (without erase)
  • Updated to latest macOS Tahoe version

Even after reinstalling macOS, the issue still persists.

Has anyone experienced a similar issue where macOS only detects one external display at a time on Apple Silicon MacBook Pro?

MacBook Pro 14″, macOS 26.5

Posted on May 15, 2026 4:54 PM

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User profile for user: Grant Bennet-Alder
Grant Bennet-Alder
User level: Level 10
143,333 points

Posted on May 15, 2026 5:32 PM

if no joy consider deleting some displays preferences files:


To access the folder using Finder for the system-wide preference

Copy and paste this string into:

Finder > Go menu > Go to Folder


/Library/Preferences


then find and delete this file:

/Library/Preferences/com.apple.windowserver


-AND- To access the folder for your-user preference

Copy and paste this string into:

Finder > Go menu > Go to Folder


~/Library/Preferences


then find and delete whichever of these two files you find:

~/Library/Preferences/com.apple.windowserver.<UUID>.plist -OR-

~/Library/Preferences/ByHost/com.apple.windowserver.<UUID>.plist


-- where [~] tilde is an active abbreviation for "current user"

-- and <UUID> is a string of hexadecimal numbers unique to your system, grouped as 8-4-4-4-8 hexadecimal digits


Restart REQUIRED after these deletions.




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4 replies
Question marked as Top-ranking reply
User profile for user: Grant Bennet-Alder
Grant Bennet-Alder
User level: Level 10
143,333 points

May 15, 2026 5:32 PM in response to Abrar_95

if no joy consider deleting some displays preferences files:


To access the folder using Finder for the system-wide preference

Copy and paste this string into:

Finder > Go menu > Go to Folder


/Library/Preferences


then find and delete this file:

/Library/Preferences/com.apple.windowserver


-AND- To access the folder for your-user preference

Copy and paste this string into:

Finder > Go menu > Go to Folder


~/Library/Preferences


then find and delete whichever of these two files you find:

~/Library/Preferences/com.apple.windowserver.<UUID>.plist -OR-

~/Library/Preferences/ByHost/com.apple.windowserver.<UUID>.plist


-- where [~] tilde is an active abbreviation for "current user"

-- and <UUID> is a string of hexadecimal numbers unique to your system, grouped as 8-4-4-4-8 hexadecimal digits


Restart REQUIRED after these deletions.




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User profile for user: Grant Bennet-Alder
Grant Bennet-Alder
User level: Level 10
143,333 points

May 15, 2026 5:26 PM in response to Abrar_95

those are bot 1920 by 1080 displays.


changing one cable for another cable is hedge against BROKEN cables, but does nothing for cables that are high enough specs.


HDMI cables you want for HDMI-only Displays (higher resolutions than 720p TV sets) are marked as Certified with an anti-counterfeiting tag and are labeled:


"PREMIUM High Speed HDMI cable" or that + "with Ethernet" (up to 4K at 30Hz) --OR--

“ULTRA High Speed HDMI cable" or that + "48G" (supports higher resolutions and backward-compatible)


Cables with No Certification tags are good for your standard 720p TV set, and not much more.


Cables 'shipped in the box' with many displays can be "lowest bidder" cables that are not up to high-end display use. Cables with no markings 'found' behind your TV set are unlikely to be good enough.


HDMI was invented for HD TV sets. it works great at its original resolution of 720i or 720p. At higher resolutions, it quickly develops issues that are complex to solve, and the cables and adapters required to solve are NOT intuitive.



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User profile for user: Abrar_95
Abrar_95 Author
User level: Level 1
4 points

May 15, 2026 5:10 PM in response to Abrar_95

One monitor is MSI MP245V.


The second monitor is Kogan KAMN27F7CSA.


This exact setup was working perfectly on my MacBook Pro M4 earlier the same day. After shutting down the Mac and turning it back on later, macOS started detecting only one external display at a time.


Both monitors still work perfectly together on my Windows laptop using the same cables/connections.

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MacBook Pro M4: Only one external display detected

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