Monterey 12.3.1 External Monitor/Display Issue - No Longer Outputting Signal

Another user in another forum pointed this out to me and it... worked?

Disconnect your monitor

Unplug your monitor

Wait a minute or two

Plug your monitor back in

Connect your monitor

This... seems to have worked for me after trying all the more complex solutions (safe mode etc.)

So this is related to a previous long-standing bug with DisplayPort, which forced all of us to go into our monitor settings and switch from DP1.4 to DP1.2 so our external monitors would work. Apparently in "fixing" this bug, Apple decided that checking autonegotiation was redundant and the user needs to manually fix things.

The solution is to set your monitor to DP1.4. For a BenQ monitor, that is going to suck, because if you don't have a valid source input, it won't give you the display settings menu. You'll need to hook up a second computer to the monitor without macOS 12.3 so the monitor has a signal, then go into the menus (System -> Advanced -> DisplayPort) and switch back to DP 1.4. Your monitors will work.

I'm so happy to have had to troubleshoot this in the middle of a workday. It was problems like this that caused me to switch from Windows to Mac over twenty years ago.

Just chiming in. MacBook Air M1 12.3 made my external display no longer be detected. I am pretty unhappy, and I need this basic function for my job.

After a few frustrated google searches and many attempts to fix, I am still stuck. Please fix Apple.

NVM. I retract this statement. When I got back in this morning it was back to no external display (thanks Apple! Happy Monday!)

This needs fixing urgently, obviously. and no, I'm not buying an Apple display.

Same issue. HP32 4K.

Not a single solution worked - neither dropping to DP1.2, nor reconnecting monitor, nor resetting NVM and this kind of stuff.

Only working solution for now is connecting monitor via dockstation hdmi port. This is the only thing waking monitor up.

Neither usb-c to usb-c nor DP to usb-c cables are working anymore.

Using Mac 10+ years first time i come across something so basic being broken ... Total disaster that affects everyone and MUST BE fixed ASAP

Updated my iMac last night. Same issue. I have two LG monitors connected via DP through a CalDigital dock. The CalDigit connects to the iMac via a usb-c connection. After the update ALL monitors including the laptop were black and would display nothing.

I had to, as suggested by others, use the Settings menu on the monitor itself to swap to Display Port Protocol version 1.2. Then disconnect and reconnect the usb-c cable from the Mac. After a reset, and reconnect monitors work again. They were both previously configured for Display Port Protocol v1.4. So - something in the 12.3 update is messing up that protocol negotiation.

Apple - you have purposefully made this as hard f*****g possible to remediate because, unlike Windows, you are so arrogant in your OS updates (that you clearly do not QA at all), that you offer no downgrade option. ALL - this is the definitive solution that I employed THREE (3) WEEKS prior and I have not had ANY issues since then,

1. Backup your entire SSD via direct connected Time Machine. If you are like me with a large SSD, congrats, APPLE FORCED YOU TOO, to spend $500+ on on an Samsung 4TB external SSD (link) where you can use this USB-C to SATA connector (link) - all regular links to US Amazon; sadly, I have no referral code/links.
2. Download version 12.1 from this site (link)
3. Create a bootable install USB key (link)
4. Boot into safe or recovery mode and re-partition your entire SSD (this wipes the entire computer FYI, but is the ONLY OPTION APPLE has made available at all...)
   1. FYI - at this point I recommend that you just hardware your laptop into your router or switch and bypass Wi-Fi; its faster and easier.
5. Set up the "new laptop" as fast a possible; your going to wipe the entire "new"/"temp" user anyway.
6. Restore Mac from Time Machine backup (link) - delete that temporary user from the prior step; wait like 4 hours maybe (that's about how long my 3.4TB SSD restore took.
7. No more issues. For weeks, blissfully easy use once again.

** Apple, you owe me 20+ lost billable hours or work, at least many hours in lost work, and over $500 for having to purchase equipment only need to remedy your insane f*** u*; congratulations, QA and OS teams - those I doubt you were the ones who made the decision to focus on continually increasing levels of completely dumbs**t; but at least we have a **** ANIMOJI...might as well be your new logo.

Similar problem with Mac mini (2018) + LG 34BL850 with USB-C.

After the upgrade, things work from the moment Mac mini boots until the first standby. When mac switches to standby and awakes from it, the display doesn't get a signal, hard restart is needed.

After the hard restart, there is a diagnostic window about segmentation fault: "window server Termination Reason: Namespace SIGNAL, Code 11 Segmentation fault: 11".

Same problem after upgrading to 12.3. Was using a portable external display driven through the thunderbolt usb-c cable. Not keep on saying no signal!!! I really regret upgrading and this is how you break customer's confidence in your product.

Same Issue here as well!

Mac Mini 2018 with BenQ PD3220U. Thunderbolt 3 used at both ends. Tried also HDMI.

Tried all solutions I have found here and at other sites.

Fortunately I did run a SuperDuper backup before upgrading to OS 12.3 so therefore I am now back at 12.2.1 again.

Does anyone at Apple read these cries out for help or do we have to mail bomb Apple Support?

Same issue. being forced to upgrade to Monterey 12.3 due to company policy and suddenly second usb-c screen doesn't work.

Config: MAC Mini 2018 + 2 x USB-C connected LG 34WK95U Monitor

Tried the following although doesn't work at all.

• both monitor's display port already downgraded to 1.2 rather than 1.4
• separate the usb-c monitor connection - now connected to the far left and far right rather than side by side

Do not want to fall back to 1 x usb-c + 1 x hdmi/display port as the colour tone is not sync

Please fix it ASAP.

Same issue here! I've got a Mac Mini 2020 with the same setup I used on my old Mac Mini: Main monitor connected via HDMI, second monitor connected via DVI->USB-C adapter. It worked there but doesn't work on this one. I already updated from 12.0.1 to 12.3 and now it displays the correct monitor information for the second monitor (previously it said that the second monitor is a 46" one?!) but when I switch it on, I still only get the "No Signal" message and then the monitor switches to sleep mode (I can still move the mouse cursor to it).

Same issue here.

Macmini i5 2018 + LG 4K display

After updating my display went black after logging. It back to work when I plugged it on HDMI port WHILE USB C is connected.

After I connected the display on two ports and I got it alive, I changed its resolution to standard res (4K zoomed to looks like 1080p) or pure 4K and it works!

On any scaled res it goes black.

But my fix is not fully functional. When my computer goes to sleep, my display doesn’t wake up.

Please guys, open the Feedback Assistant and report the bug to Apple

I have the same issue with my iMac when I upgraded it to macOS 12.3 from that time my external USB-C monitor is not detected and displayed a "No Signal" error. while it works with some of the USB-C to HDMI adaptors.

The same monitor and the same USB-C cable is working properly on my MacBook that its macOS is not upgraded.

Another interesting thing is that even some of the USB-C to HDMI adapters are not also working with my upgraded computer while those are working with my MacBook with a downer macOS version!

I already check all the things on the apple checklist and had talked 3 times with the apple support.

If somebody has a solution please let me know.

Same issue here with a MacBook Pro 13-inch and an external monitor from LG which is connected with DisplayPort. Since the update to 12.3 there was no signal.

I tried different solutions but they laat one was working for me to move from DisplayPort to HDMI