macOS 12.3 update triggered external or second monitor issue using USB-C, says 'no signal output' (potential workarounds inside)

Unveiled in June last year at the WWDC, Apple recently released the latest incremental macOS Monterey update to version 12.3. It introduced features such as Universal Control that enable users to use a single mouse and keyboard across their Mac and iPad.

They also added support for Spatial Audio on devices with the M1 chip as well as the ability to add episode filter for Podcast season.

While the new features are a welcome addition, a bug is making it impossible for those who upgraded to macOS 12.3 to use the second monitor and are getting a ‘no signal output’ message when connected via USB-C (1,2,3).

Users say that their secondary or external display went black after the update and is undetectable in System Preferences when connected.

The problem seems to be angering many productivity-focused Mac owners who often work with multiple monitors.

Below are some reports from macOS 12.3 users affected by the ‘no signal output’ error message when connected to a second or external monitor via USB-C.

After updating my Mac Mini today to 12.3, my monitor now no longer displays an image via USB-C, just keeps saying on no signal on the monitor. I have tried HDMI and same issue. The odd occasion it will display a picture but once I shutdown or restart the mac mini it does not display a picture. The mac is booting up. I have had to resort to connecting it to my old TV with HDMI connection. This is so frustrating I have tried resetting the SMC which had not appeared to work, also tried downgrading the displayport version from 1.4 to 1.2 (on the odd occasion I did get a picture) but that has not worked either.
(Source)

Hi, like others I have an issue with Monterey 12.3 in my MBA m1. After the update my “vintage” apple thunderbolt monitor is blank (black screen no apparent backlight), the monitor is recognized by macOS, meaning, if I go into settings-display I can see the monitor show up right name and all, I can even loose sight of the mouse pointer if I move it to the edge side where the screen is supposed to be (left in my case), every other thing on the monitor works, the camera, the speakers, the USB ports even the Mic, just not the screen.
(Source)

In case you did not know, this is not the first macOS update that has broken multi-monitor functionality. Last year, macOS Big Sur 11.1 update reportedly broke support for external 4K monitors.

As it turns out, a bunch of users are also saying that the recent update has broken wake from sleep function for external monitors as well.

While Apple is yet to comment on the matter, we came across a bunch of workarounds that seem to be working for some. The first one involves using the HDMI cable to connect the monitor.

Another workaround suggests switching the primary monitor with second one in system settings. The third solution requires users to disconnect the USB-C monitor, booting up using the monitor connected via HDMI and plugging it back.

And if the aforementioned workarounds don’t help, you can try lowering the DisplayPort version from 1.4 to 1.2.

I’ve solved this problem (on 2022-03-15). On my monitor (LG LCD 27 27UN880-B IPS) I’ve went into settings, and I’ve lowered the DisplayPortVersion from the default v1.4 to v1.2. As soon as I’ve lowered the monitor’s DisplayPortVersion, my Mac with OS X 12.3 has started recognizing the second display correctly. It seems that the new OS X update has issues with a DisplayPortVersion 1.4 protocol (has faster data rate, faster refresh, and stream compression). Hope this helps.
(Source)

We hope Apple takes a look at the matter and fixes the issue as soon as possible since it is making it impossible for many to use their multi-monitor setup. If and when they do, we will update this space to let you know so stay tuned.

Note: We have more such stories in our dedicated macOS Section so be sure to follow them as well.

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