External Display Only Works in Presentation Mode, Can’t Extend Desktop

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Level 1

4 points

External Display Only Works in Presentation Mode, Can’t Extend Desktop

Model: MacBook Air (M4, Tahoe)

Issue Description:

The problem started after I stopped mirroring my display from the menu bar by clicking the display icon. Since then, I’ve been unable to extend my external monitor again. The external display only works in presentation/mirroring mode, not in extended mode.

Troubleshooting Steps Tried:

Reinstalled macOS
Ran the following commands to reset WindowServer preferences:


sudo rm /Library/Preferences/com.apple.windowserver.plist
rm ~/Library/Preferences/ByHost/com.apple.windowserver*

Tried multiple debugging steps suggested by ChatGPT

Despite all this, the issue persists and the external monitor still won’t extend.

Please advise what else I can try to fix this issue or how to restore extended display mode.

Posted on Jan 25, 2026 8:32 AM

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Answer 1

Top-ranking reply

Servant of Cats

Level 8

35,573 points

Jan 26, 2026 11:23 AM in response to _theray

_theray wrote:

The hub i am using is : "Portronics Mport One USB C Hub Dock (9-in-1) with 4K 60Hz HDMI, 3-Port USB, HDMI On-Off Button, 100W Type-C Charging, Card Reader, 3.5mm AUX, Type C Plug for Laptop, Mac, PC (Grey)"

That text string matches this Amazon (India) listing, and it looks like the manufacturer's description of this hub is here ("Portronics Mport One") .

This appears to be a plain USB-C hub. I don't see any sign of "troublesome" features like multiple video outputs, the ability to use the hub to connect a monitor to a USB-A host, etc. that might point to use of DisplayPort MST or to the use of some second-class "workaround" that relies on installation of a special driver. My guess is that this hub drives its HDMI port off of your computer's USB-C (DisplayPort Alt Mode) signal in a standard way.

So far, so good.

There is one unusual feature: a "HDMI Display Switch" that lets you "switch [the] HDMI connection on [and] off," using a single button press.

Two thoughts:

If the "HDMI Display Switch" is turned off, this would explain why the Mac could not detect the display: the hub would be blocking that. You may want to check and make sure that the switch is turned on.
When you change the switch from the "off" position to the "on" position, that might not be enough for the Mac to know that there is a display that you need to query. After turning on the switch, you might need to take some action like pressing the Shift key, using System Settings > Displays > Detect Displays, or turning the monitor off and back on so that the Mac notices the monitor, queries it, and establishes a display connection.

By the way, that HDMI Display Switch on the top of the display seems to be in a place where it would be trivial for a cat to change the position of the switch if the cat were to walk over the top of the hub …

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Answer 2

_theray Author

Level 1

4 points

Jan 27, 2026 1:40 AM in response to Servant of Cats

Thank you very much for your reply and your suggestions. They were truly helpful in clarifying several points and resolving some of my doubts. I sincerely appreciate your time and support, and I am very grateful for your help. Thank you once again.

I just fix it by running these commands:

# Remove system-level display preferences
sudo rm /Library/Preferences/com.apple.windowserver.plist

# Remove user-level display preferences
rm ~/Library/Preferences/ByHost/com.apple.windowserver.*

# Remove additional display caches
rm ~/Library/Preferences/com.apple.spaces.plist
rm ~/Library/Preferences/com.apple.desktop.plist

and then restarting it. Now everything is working fine.

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Answer 3

Jan 25, 2026 6:29 PM in response to _theray

Which hub are you using?

If it is a plain USB-C hub that relies on DisplayPort Alt Mode, and that only provides one place to connect a display, it should be using the DisplayPort Alt Mode signal from the Mac to drive its HDMI port. In which case, it should be possible for the Mac to detect the presence of the external display, if the display is turned on (and set up so that it uses the input from the hub/Mac) at the time the Mac attempts to query the display.

What happens when you go into System Settings > Displays, hold the Option key down, and click the button that has changed to read "Detect Displays"? Does the Mac see the display at all?

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Answer 4

Jan 25, 2026 9:08 AM in response to _theray

That screenshot does not show the presence of a second display, so it's unclear whether your external display is a real hardware monitor, or an AirPlay display. Either way, see:

Extend or mirror your Mac desktop across multiple displays - Apple Support

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Answer 5

_theray Author

Level 1

4 points

Jan 25, 2026 4:53 PM in response to Servant of Cats

my external display is real hardware monitor, i have connected it using type c hub with hdmi, yes even when i connect second display is not been shown in Display setting. Although external monitor is working in presentation mode only, but i want to used it as external monitor.

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Answer 6

_theray Author

Level 1

4 points

Jan 26, 2026 6:39 AM in response to Servant of Cats

The hub i am using is : "Portronics Mport One USB C Hub Dock (9-in-1) with 4K 60Hz HDMI, 3-Port USB, HDMI On-Off Button, 100W Type-C Charging, Card Reader, 3.5mm AUX, Type C Plug for Laptop, Mac, PC (Grey)"

When i click Detect displays, Mac doesnot see the display at all.

Everything was working well till Jan 25, and from menu bar i click mirror icon and then clicked "stop mirroring" and from then my monitor is not being detected

[Edited by Moderator]

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Answer 7

_theray Author

Level 1

4 points

Jan 27, 2026 12:13 AM in response to Servant of Cats

I have tried thought 1 and 2, multiple times but its not working, is there any solid solution to fix it.

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