LG UltraFine (27MD5KL) monitor no longer shows up as a detected display but provides power.

Question

LG UltraFine (27MD5KL) monitor no longer shows up as a detected display but provides power.

I have a MacBook Air (M3 15inch) and a LG UltraFine (27MD5KL) monitor. They are connected with a thunderbolt cable.

The monitor has worked as an extended display until two months ago.

The monitor will charge my MacBook but has stopped showing an image.

The monitor does not show up in settings as a connected screen.

I have tested the connection with a new thunderbolt cable.

I have tested the connection with a different MacBook.

I have power cycled both devices.

I have not been able to download firmware for the monitor because LG does not offer this option on their website.

My MacBook is running the latest OS, Tahoe 26.2

I have seen reports from other users having the same problem.

Posted on Dec 18, 2025 9:55 PM

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Answer 1

TheLittles

Level 10

203,031 points

Dec 18, 2025 10:09 PM in response to seamonster.spacestation

"LG UltraFine (27MD5KL) monitor no longer shows up as a detected display but provides power.: [...]The monitor does not show up in settings as a connected screen.[...]"

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Troubleshooting a Black Connected Mac Screen:

A. Verify the Monitor's Existence:

Verify that the sparks are seen in System Information. If not, then you might have to resin tall the macOS to ge the driver's back.

Hold Down: [option key + click Apple menu)
Select: System Information
Click: Graphics/Displays
Verify: [this screen] is seen.

B. Mirror the Screen to this External Display:

Performing the following will mirror the Home Screen, and allow you to use it as if it were you laptop's screen.

Without Touchbar: Hold Down [command + F1]
With Touchbar: Hold Down: [command + dull screen]

C. Remove All Attached Devices:

Boot up with nothing plugged in. See if the circuity equals out.

D. Boot in Safe Mode: [Hold Down: shift key, upon boot], In Safe Mode, Login Items do not run at login, certain preferences are set aside, and damaged system files are then reset. So, once booted in to Safe Mode, wait 30 seconds, and then boot up normally, attempting another update install.

E. Reset the SMC and your NVRAM: (Apples to Intel-Based Mac's Only): Sometimes when changes are made to the system(i.e. updates), system configurations (i.e. for Screen) become manipulated, technically. So, reset the SMC and NVRAM

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Answer 2

TheLittles

Level 10

203,031 points

Dec 18, 2025 10:11 PM in response to seamonster.spacestation

"LG UltraFine (27MD5KL) monitor no longer shows up as a detected display but provides power.: [...]My MacBook is running the latest OS, Tahoe 26.2 I have seen reports from other users having the same problem."

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To the OP and all those Affected...

Troubleshooting a Black Connected Mac Screen After an Update:

Report this to Apple:

Do your Part: Inform Apple of your feedback of this issue. Include how you’ve troubleshot this, and your results. Apple wont get back to you directly, but the more feedback they receive from its users, the more likely they will know what needs to be fixed, and what bug fixes to include in, and macOS versions to come. Apple with know nothing of this occurrence, if you don't report it to them.

Go Here: Feedback - macOS - Apple
Select: "Bug Report" for the "Feedback Type"
Select: "Software/Firmware Update" for the "Feedback Area"
Comment: That this all began after installing an update.
Proceed from there as necessary

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