macOS Sequoia 15.3 wont let me detect my second display

Ok I fixed it: after trying everything I could read everywhere, the solution for me was very simple and strange:

I pulled the usb-c thunderbolt cable out of my second screen, then flipped it (so the usb-c thunderbolt that was in the MacBook go into the screen, and the side that was in the screen, I put into the MacBook), and then it worked again.

I'll also list other possible solutions that worked for other people, maybe it works for you (it didn't for me):

1. Disconnect and Reconnect All Devices:

• Shut down your Mac and disconnect all peripheral devices, including your external monitor.

• Wait for about 5 minutes.

• Reconnect your external monitor and other devices, then start your Mac.

• This method has been effective for some users experiencing similar issues.  

2. Reset NVRAM/PRAM:

• Resetting the NVRAM/PRAM can sometimes resolve display-related problems.

• To do this, restart your Mac and hold down the Option, Command, P, and R keys simultaneously for about 20 seconds.

• Release the keys and allow your Mac to continue starting up.

• This process can help with various hardware-related issues.  

3. Detect Displays Manually:

• Go to the Apple menu and select “System Settings.”

• Click on “Displays” in the sidebar.

• Press and hold the Option key to reveal the “Detect Displays” button, then click it.

• This can prompt your Mac to recognize the external monitor.  

I hope one of these solutions works for you. Good luck!

It seems that many people, including myself, are experiencing the same issue. After installing the new OS Sequoia 15.3, my second monitor, which I previously connected via a Thunderbolt cable, is no longer being detected as it used to be.

This issue is causing me significant trouble, and I want to know if anyone has already found a fix for it.

I have also tried to find a way to downgrade the OS, but I couldn't find any clear instructions on how to do it.

I would like to request help from anyone who is facing the same issue or has already solved it to share their solution with me.

I have no idea why this problem occurred, how long I have to wait for a fix, and I sincerely hope that Apple will resolve this issue as soon as possible.

Sad!

To be constructive, after rebooting and tearing up a bunch of wiring, all with no effect, I installed an app (from the Apple app store) called "Display Menu". In my case, I could tell that the MacBook was *kind-of* seeing my external monitor (which as with everybody else here has been working for months before 15.3). I could tell this because the monitor, instead of showing the TV error about there being no HDMI signal, was showing a message clearing coming over HDMI from the mac telling me to choose the display mode (in a weird way that makes no sense). The "Displays" settings thing, the MacOS one, however did not see the monitor. With that "Display Menu" app installed, I got a little widget in the menu bar that *did* see the external monitor, and it let me choose it as an extended display. Now it works fine.

Again, I want to be clear in my opinion here (which is very important :) that this is an OS issue. Maybe Apple has some idea of a new/improved/different feature, but it does not work properly now whether it's a good idea or not.

Re: “My question now is does Apple actually read this support network.”

This is a user to user forum. Apple largely is not here except to moderate it, and is unlikely to see reports of problems unless you contact Apple Support or submit feedback on Apple’s feedback page.

There are other users (not Apple employees) here who can help to troubleshoot causes like trying to use more displays than a given Mac supports. But if you are experiencing problems with a supported configuration, especially ones that seem to be tied to a macOS update, you need to get that information to Apple. Other users here can commiserate, but do not have access to macOS source code, etc. to fix bugs. We are as dependent on Apple as you are.

You may want to include a link to this thread or others that contain detailed problem descriptions when you contact Apple. But they’re not going to notice detailed problem reports here unless you call their attention to them.

Hello everyone. This solution worked for me. I panicked when after updating to Sequoia 15.3.1 my hub stopped being detected by my Imac M1. I use the hub for the Ethernet cable, the SD cards, a couple of USB connections for external SSD from time to time, and my second screen which I almos depend on. Try this before deleting files!

This just happened to me two days ago. I thought my cable had failed, and I ordered a new one. Next day, it after the cable arrived and replacing the cable proved useless, I searched and found this thread.

I first tried moving just the more narrowly focused file at

mv /System/Volumes/Data/Users/<myusername>/Library/Preferences/ByHost/com.apple.windowserver.displays.<hexadecimal-uuid-value>.plist ~/Desktop

and rebooting, but nothing changed.

Then I moved the file at the more general /Library/Preferences location:

sudo mv /Library/Preferences/com.apple.windowserver.displays.plist ~/Desktop

and rebooted, and all is well.

What is crazy is I had run the OS update a few days prior, and had no issues when I plugged the external monitor in. It was only when I switched inputs & cables for the external monitor that the problem suddenly appeared, but even switching back to the original input and cable, the issue persisted. FWIW I'm using a USB-C to DVI cable to drive a 49" Samsung Odyssey G9 from an M3-equipped MacBook Pro; the cable I'm using allows the monitor to run at 120Hz (limit of the Mac hardware). None of that matters for this issue. But I'm including it in case doing so helps others find this post when they search.

Here is my problem and how I fixed it.

The problem:

Monitor connected via hub would not show anything, but I could move my mouse to it and some windows were moved there for sure, so my mac recognized it, but did not show anything. If I connect the same monitor via hdmi directly it worked, so whatever monitor is connected via hub did not work.

Solution:

May not work for everyone.

1. Go to System Settings.
2. Displays
3. If you can see a monitor you are having problem with, click on it and change the color profile several times, eventually it may work again, from there you can change the color profile to the default one. Attaching the screenshot.

P.S.: Not sure if it is a temporary solution or it fixes the problem completely, just fixed it and decided to share. Good luck.

edit: Just checked. When I disconnect and reconnect the monitor the problem is the same, but now I can fix it pretty easily by chaning color profile or refresh rate (apparently does the same thing I guess- refreshes some configs on laptop side).

I have the same issue here. I escalated this to Apple support Germany to increase more awareness. I hope this will be fixed soon.

To Apple, when will the second external monitor issue be fixed? I have MacOS 15.3.1 on my M1 MacBook Pro. I have the same problem others have encountered. I've tried all the proposed solutions and it still does not work. I have been using two external monitors (and my MacBook pro monitor) for about a year with earlier MacOS versions with no issues.

Unfortunately, the deletion of the plist file did not work for me...really wish it had!

Since I had NO trouble prior to installing the update, I have no choice but to point at the update as the problem. I also wish there was an easy way to rollback updates that didn't require erasing everything on my Mac Mini M1 and reinstalling everything again...

UPDATE: I just returned from purchasing a new HDMI cable - the cable swap didn't work either. I'm still getting intermittent failure on the monitor where it goes black and then the display returns after a brief period of time (a few seconds to a few minutes). I depend on my big monitors quite a bit, and I am so NOT used to Apple OS updates breaking things upon installation. I left the PC world behind partly for that reason and thought my days of fighting with drivers and updates were mainly behind me...alas, no such joy...

So, Apple - when will we see a patch/fix/solution for this issue?

I was forced to update my mac yesterday (too "old" of OS to use microsoft product... apparently). After the update, not able anymore to connect my monitor.

thank you for the info on the file to delete. That fixes my problem too.

APPLE... STEP UP YOUR GAME FOR F*** SAKE. How can you allow such a problem to happen. For all the non technical people out there, this is going to create a mayhem of frustration and an increasingly bad User experience of your product.

I managed to fix it. It was a combination of the discussed solutions in this thread.

• Disconnect the non working displays from usb c as well as power for some minutes
• Delete the library/preferences/byhost/apple.windowserver.displays.plist file
• Delete Trash

I repeated this procedure 3 times until each display works.

I wrestled with this problem after upgrading to 15.3.1. Was about to use Apple Support to erase 15.3.1 and go back to an older version when I stumbled on a fix after reading all the comments in this thread. The display monitor is black - but you can see it in system settings/displays. When I change the refresh rate from 75Hz to 60Hz and then wait about 5-10 seconds, the monitor comes to life. It's definitely a lower quality display, but at least it's working now. Here's a picture of what worked for me. LMK if it helps to solve your problem! Also, Apple still needs to solve this software issue as we need our external monitors to be the high definition we purchased!!

It was easy to just trash this file: apple.windowserver.displays.<hex_string>.plist : and restart and problem solved.