macOS Sequoia 15.3 wont let me detect my second display

For anyone who thinks they've fixed this by doing X, Y or Z:

Wait a few days before coming to any conclusions. The thread is full of people saying they have fixed it by doing something, only to return shortly afterwards saying the problem has returned.

sudo rm -rf /Library/Preferences/com.apple.windowserver.*

That terminal command "worked" for me, I think.

However, just in case it's relevant, here's what I also did:

1. Previously, I had rebooted my laptop about 15 times as I tried various "solutions,"
2. I complained to co-workers who use Linux and Windows machines while explaining why I couldn't focus on my tasks presently,
3. In Displays preferences, I hit "Detect Displays" roughly 30 times (no feedback; the button might be a "hello world" PoC button hooked up to nothing),
4. I previously deleted numerous com.apple.windowserver.<hash>.plist files, emptied trash repeatedly,
5. As my body language became slightly more aggressive and fed up, I made eye contact with other co-workers who were happily using external monitors on hardware that was a couple thousand dollars cheaper,
6. After running the above command, I rebooted while holding down Option+Command+P+R just in case that did anything (no feedback from UI; it may be another placebo),
7. Finally, during the last reboot, I was actively focusing on and pondering if using Macs is really worth the constant deprecations, extra costs for hardware that no longer "just works," $100+ dongles, and the consistently declining UX.

Something in all that worked.

Having this same issue...

Macbook Air 13" 2025 (Mac16,12)
Sequioa 15.5 (24F74)
Dell Utrasharp U2722DE connected via USB-C 

I've tried deleting `com.apple.windowserver.displays.plist` but this doesnt seem to have any effect. The monitor works perfectly fine on my Macbook Air 2022 running Sonoma.

On the Sequia Macbook, If I shutdown and power cycle the monitor, sometimes when I then reboot the computer the monitor appears and works as expected, but as soon as the computer goes to sleep, or if I disconnect and later reconnect the monitor, it doesnt show up.

I've also updated the firmware on the Dell and installed Dell's display software on the MacBook 2025 to no avail.

While upgrading from Sequoia 15.5 to 15.6. on an M4 Pro Mac Mini with two LG TVs for monitors with one attached via HDMI and the other via Thunderbolt 5 port with converter to HDMI, the install stopped for several hours. I detached the monitor connected via the Thunderbolt 5 port and the install resumed. I think this also suggests a USB subsystem problem in MacOS 15. (Apple please fix this!)

Today After spending 40 minutes on the phone with apple, they just say that it's not supported by machine, 2 monitors just with the lid closed. It's the end for me.

@geapgr - Are you saying this was a permanent solution for you? Were you experiencing this issue every time the system went into sleep mode - which is only where I am seeing it? Will of course give it a try, but sadly have just made power cycling the HDMI monitor part of the startup process. Hoping for 15.3.1 and a resolution!

Hi. I experienced the problem directly coming into 15.3. Couldnt solve it whatever i did. Called apple in greece and they provided this remedy. Working fine since even after shutdowns and restarts. Cheers

It's very clear there is an issue with this update, the internet is full of it, already at least more than a month. No solutions worked for me. This is 100% a software issue on apple's side. I need the second screen for work and it affects my productivity a lot. When will Apple fix it?

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!

I have MBP M4 Pro and two external displays. One Dell and another one portable display via type-c.

Right after macos update the second display went off. And I tried everything here, restarts, unplug, all ports etc.

It doesn't work. But Dell is working fine. Before the update, on 15.2 everything worked very well.

Just adding my voice to the chorus of infuriated customers here! Brand new iMac connected to my Apple thunderbolt display from a few years ago - it worked great until I updated to 15.3 and BOOM the display is no longer recognized. I tried connecting it to my 2023 Macbook Pro running 15.3, same results. I've tried all of the troubleshooting methods and nothing has worked. Meanwhile, a 10 year old LG monitor is recognized by my new iMac immediately via HDMI with no issues. So for now, my awesome Apple display gathers dust while my much-less-awesome old LG monitor fills in.

Ridiculous.

Got excited when I saw that 15.3.1 was released today - really hoped that there would be a fix for this VERY ANNOYING AND OBVIOUS software issue. But alas, my tunderbolt display is STILL not recognized.

I used to have two external monitors connected to my Mac: one via HDMI and another via USB-C. After updating to version 15.3.1 (24D70) yesterday, macOS now only recognizes one of them. The second monitor turns on but only mirrors the first one, and I can no longer extend the display.