Level 1

6 points

External displays not detected after macOS Tahoe 26.5 update

Is anyone else having issues with external monitors after updating to macOS Tahoe 26.5 (25F71)?

My setup was working perfectly before the update. I'm using a MacBook Pro M5 Max with a Satechi Slim Multiport Docking Adapter and two external monitors. Right after updating, macOS started only detecting one monitor at a time. I thought it might be the dock, but I tried a completely different hub and had the exact same issue.

Around the same time I was using clamshell mode a lot, so I'm not sure if that's related, but things have only gotten worse since then. One of my monitors (an AOC curved monitor connected via HDMI) now isn't detected at all. It doesn't show up in System Information > Graphics/Displays, and macOS acts like nothing is connected.

The weird part is the monitor definitely works. I've tested it with another device and it connects straight away.

So far I've tried:

Different hub/dock
Different HDMI cables
Restarting multiple times
Deleting display/WindowServer preference files
Power cycling the monitor
Disconnecting and reconnecting everything from scratch

When I plug the AOC in, my Mac screen briefly goes dark grey like it's trying to detect a display, but then nothing happens and the monitor never appears.

I've also found a bunch of posts from other people having similar issues after updating to Tahoe 26.5, especially with external displays, docks, and clamshell mode.

Just wondering if anyone has found a fix yet, or if this is looking like a Tahoe 26.5 bug?

MacBook Pro 14″, macOS 26.5

Posted on Jun 2, 2026 2:04 AM

Top-ranking reply

ericn2345

Level 1

4 points

Posted on Jun 30, 2026 11:29 AM

I did a bunch of combos with my 2 LG 32" 4K 3-4 year old monitors. and two different M5 pro max's, and two cables (USB4/60W/Thunderbolt 3 cable and a USB4/240W/Thunderbolt 5 cable).

Everything works flawlessly with my M1 Mac Pro, but the M5 Max's would not generally recognize the display, or their power over USB. An odd exception is that one of the M5's would work for the first time plug in after a reboot, and then stop recognizing the monitors, the other one just did not see the monitors.

Here's the annoying procedure I use now to repeatably get the LG monitors to work:

==> Using the Thunderbolt 5 cable (and MacOS 26.5.2 - I expect ..1 is the same)

Go to settings => displays

Press "Options" to unhide the ""Detect Displays" button
Click on the ""Detect Displays" button a few times
unplug the USB cable
replug in the USB cable to the same port

And the display would show, and power will flow as long as the cable stays plugged in, and the power to the monitor on. [note: unplugging within the first minute or so after my above procedure does not lose the monitor connection]

Results with the older USB 4 cable were less consistent.

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25 replies

Aug 26, 2026 12:09 PM in response to Benjamin Ing

if you have EXACTLY the same equipment as the original poster, and running EXACTLY the same version of MacOS on the same Mac, your solutions should be available by a careful reading of all the postings above..

Otherwise, you should start a NEW discussion to get the personalized attention your issues deserve.

Starting a new discussion will allow Readers to think hard about your exact situation and address the exact circumstances you are facing. It also allows YOU the decide the Title of the discussion, which is what might attract Readers with the right insights to apply to your problem.

https://discussions.apple.com/post/question

Jun 14, 2026 7:17 AM in response to 1d_gamer123

There have been No new widespread pervasive reports of issues with external display support in MacOS 26.5.1

If this were a widespread problem, there would already be dozens of discussions and hundreds of users posting here.

Connecting displays to a modern Mac is a complex process, with MANY potential pitfalls.

Readers are willing to do a deeper analysis with anyone willing to post the make&model of their display(s) or a link to the detailed specs, AND the exact cables, adapters, and docks being used to make the connection.

Jun 14, 2026 10:31 AM in response to ProfLeslieSmith

Dell SE2417HGX appears to be a 1920 by 1080 display at 8 bits/color with refresh rates 56 to 76 Hz.

interfaces include:

2x HDMI 1.4

Analog VGA

Acer XB240H appears to be a 1920 by 1080 display at 8 bits/color with refresh rate of 144 Hz

interfaces include:

HDMI 1.4

DisplayPort 1.2

DVI dual link

Analog VGA

Your DP2HDMI 13850 adapter yields no search results.

Generic DP2HDMI suggest an adapter that produces HDMI as its output. As long as resolutions are very low, that can work, but USB to DisplayPort offers more bandwidth for DisplayPort-capable displays. this can provide better support for displays around 4K in size, converting using a dongle form a USB-C port.

Jun 15, 2026 3:25 PM in response to ProfLeslieSmith

<< In the end my conclusion was: OS26.5.1 is a bit choosy about what monitors it can drive. >>

Based on the experiences of many other users on these forums, there is no support for your wild guesses.

Xendren

Level 1

8 points

Jun 27, 2026 7:54 PM in response to 1d_gamer123

I found an answer in Apple Community last week that suggested there was a corrupt display preference file left during the install of Tahoe 26.5.1. I followed the steps, and it fixed my MacBook Air. I cannot find the post any longer, but I took a screenshot of the post and steps. This has been the only thing that has worked on all of my Macs. Hopefully, it helps someone else.

Aug 17, 2026 3:44 AM in response to Xendren

This fix worked for me with Macbook Pro (M1) and Alogic 27" monitor. I only removed the file under my home directory (i.e. didn't do the sudo commands suggested), and a restart. This has happened before after Tahoe updates.

Jun 14, 2026 8:24 AM in response to ProfLeslieSmith

The Acer is an XB240H, manufactured in 2015. So yes, really quite old.

Jul 16, 2026 1:52 PM in response to Xendren

Thanks for this, going to try it tonight and see if it resolves the issue.

meggan33

Level 1

8 points

Jul 24, 2026 6:49 AM in response to yosoynev

How did you do this? How can i go back to 26.5.1? I am having the same issue

Aug 6, 2026 2:45 AM in response to Xendren

Thanks this work.

External displays not detected after macOS Tahoe 26.5 update