I recently updated my MacBook Pro 14” (M2) to macOS Tahoe. Since the update, my external display is not being detected when connected via HDMI. However, if I connect my iPad as an external display, both the iPad and the external monitor work. Once the iPad is disconnected, the external display also stops working.
[Re-Titled by Moderator]
Original Title: Tahoe external display not detected
MacBook Pro 14″, macOS 26.0
Hi everyone,
Just spent 2 hours on this and found a fix that doesn't involve buying a USB-C adapter, so I figured I'd share since every thread I read ends with "just get a dongle".
My setup: MacBook Pro 14" M2 Pro, macOS Tahoe 26.5, Samsung monitor over HDMI plugged directly into the Mac's built-in HDMI port. Classic symptom, the monitor powers on but stays black, and the Mac doesn't see it at all. Nothing in System Settings, nothing in system_profiler SPDisplaysDataType, nothing in IORegistry. The same HDMI cable works fine on my TV, and the monitor used to work with this Mac before the Tahoe upgrade.
I tried everything you usually find on forums: multiple HDMI cables, rebooting with the monitor already plugged in, updating macOS (26.4.1 then 26.5), disabling VRR on the monitor, Option+Detect Displays in System Settings. Nothing changed.
What ended up working is one command in Terminal, no sudo needed:
mv ~/Library/Preferences/ByHost/com.apple.windowserver.displays.*.plist ~/Desktop/
Then plug the HDMI cable in, restart via the Apple menu, and on boot the monitor is detected right away.
Why it works. macOS keeps a cache of every display it has ever seen in this file. On my Mac there were 11 configurations stacked up across 8 different displays (old TVs, meeting room projectors, previous office monitors, you name it), and several of them were in a clearly broken state: dimensions of 1x1 pixels, origin coordinates at -3200, a mix of Sequoia and Tahoe formats in the same file. Tahoe became way stricter about validating this file, where Sequoia would just silently ignore invalid entries. So the entire display detection pipeline gets stuck on the first malformed entry it hits, and the HDMI handshake never even starts with a new monitor.
The mv sends the file to the Desktop instead of deleting it, so you have an automatic backup. If anything goes weird you can put it back:
mv ~/Desktop/com.apple.windowserver.displays.*.plist ~/Library/Preferences/ByHost/
Hope this helps someone.
kokularaj wrote:
Thanks for your reply. I intended to connect only one external display via HDMI, while my iPad is connected as a display over Wi-Fi. Interestingly, when I connect the iPad as a display, the HDMI-connected external monitor also works. This makes me believe it’s not a cable issue.
To be proactive you can file a bug report / submit your Apple Feedback here: Product Feedback - Apple
Braunie-
If you do not have a recent local, disk-based backup, your computer is like a ticking Time bomb. You are only one disk failure, one mainboard failure, one crazy software, or one "oops" away from losing EVERYTHING! Drives do not last forever. It is not a question of IF it will fail, only WHEN it will fail. In addition, you never know when crazy software or Pilot Error throws away far more than you intended.
If you are using another direct-to-disk backup method that you prefer, and you currently have a recent disk-based backup, that is great. If not, you should consider using Built-in Time Machine. Take steps to acquire an external drive as soon as possible. If you buy one, a drive 2 to 3 times or larger than your boot drive is preferable for long term trouble-free operation. Do not pay extra for a drive that is fast. (You can get by for a while with a "found" smaller drive if necessary, but it will eventually become annoying).
Attach your external drive and use
Settings > General > Time machine ...
... to turn on Time Machine and specify what drive to store your Backups on. It may ask to initialize the new drive, and that is as expected. APFS format is default format if running MacOS 11 Big Sur or later.
Time machine works quietly and automatically in the background, without interrupting your regular work, and only saves the incremental changes (after the first full backup). Time machine backs up your machine — including every connected drive that is in a Mac compatible format. it can not back up Windows format drives.
Time Machine's "claim to fame" is that it is the backup that gets done. It does not ruin performance of the rest of the computer while doing its backup operations. You do not have to set aside a "Special Time" when you only do backups. When you need it, your Time machine Backup is much more likely to be there and be current.
How to use Time Machine to Backup or Restore your Mac:
Back up your Mac with Time Machine - Apple Support
it's the software. I am running an older thunderbolt 2 apple external, been using a TB2>USB C adapter (from apple) for years with no problem. as soon as I upgraded to Tahoe it stopped working. I tried a new adapter to be sure, nothing.
tyler.komar wrote:
it's the software. I am running an older thunderbolt 2 apple external, been using a TB2>USB C adapter (from apple) for years with no problem. as soon as I upgraded to Tahoe it stopped working. I tried a new adapter to be sure, nothing.
exactly what model older apple display?
exactly what adapter is this?
How long is the cable?
You're right. LG 40WP95C owner here, connected to M1 Studio Max. Sequoia 15.7.2 and Tahoe 26 changed the game when it comes to Thunderbolt connectivity. The LG cables that I've been using for the past years, connected to the same M1 Studio decided to quit, because Apple changed the software. So I went and bought the expensive TB5 Apple cable and a cheap Anker one. Both work now. So, you're ok with Anker or any that is 'certified' Thunderbolt cable.
We have 12× SD5000T5 EQ Thunderbolt™ 5 docks at the office, all paired with premium StarTech USB-C cables.
Everyone who updated to macOS Tahoe 26.1 (with M2 Pro) is having issues not a single dock works anymore.
Seriously, Apple? These docks cost nearly €500 each, not even counting the cables.
How do you mess this up so badly? And don’t even get me started on the memory usage in Tahoe 26.1.
I’m honestly at the point where I’m considering switching to Microsoft… these display issues are driving me insane.
Apple has just published a clarifying article about Variable Refresh Rate displays.
It seems not all Macs support that feature:
Use an Adaptive Sync external display with [some models of] Mac
https://support.apple.com/en-us/102144
what model 38-in LG display?
how long is that USB-C cable?
Thanks for your reply. I intended to connect only one external display via HDMI, while my iPad is connected as a display over Wi-Fi. Interestingly, when I connect the iPad as a display, the HDMI-connected external monitor also works. This makes me believe it’s not a cable issue.
I have a high quality USB C cable, and new 38 inch LG monitor I've been using with my macbook pro 2024 14" model. I've just upgraded to MacOS Tahoe, and now my macbook doesn't recognise my USB-C monitor when plugged in. It was working flawlessly before the upgrade. Extremely frustrating!
Not just external display. Cannot connect any of my midi devices either. In practise this all rendered my Mac useless. Losing thousands because of this as I needed to turn down work. Shame.
I guess the only way is to save anything important like all my music projects to external hard drive / pen drive and try to wipe everything clean + make fresh install. That will be nice few days.
Complete mock up. Shame on you Apple.
I also experience the originally described issue. (I deeply regret installing Tahoe so early. This is by far not the only...)
veronyka98's solution worked once for me. But after stopping the mirroring for one window, all mirroring stopped. And now the MacBook does not show any indication of the external display being connected anymore. Even running through those commands again doesn't bring any mirroring back.
[Edited by Moderator]
Tried the terminal commands to no avail. The problem is that it sometimes works. Tried on two different monitors. Seems to have a long delay and then it might come on. Othertimes, it comes on right away. I'm surprised there isn't an upgrade fix to this yet...will try ordering some new cables next, I suppose.
<< SD5000T5 EQ Thunderbolt™ 5 dock.
all paired with premium StarTech USB-C cables. >>
The lead-in cable for that Thunderbolt-5 dock must be a genuine Thunderbolt-5 cable no longer than 0.5 meters. if those USB-C cables are used as lead-in cables (between Mac and Dock) you will lose most capabilities of those docks.
if you are using USB-C cables to your displays, they are limited to ONE meter, maximum.
I'm using the same usb-c cable that came with my FIFTEEN HUNDRED DOLLAR Apple display. If upgrading to Tahoe was going to cause the display to no longer work, then Apple should have alerted the community.
[Edited by Moderator]
External display not detected after macOS Tahoe update via HDMI
