After Sequoia 15.3 update, external monitor is not recognised by my MacBook Air

This has happened to so many people on so many websites that have this discussion it doesn’t matter if you have an iMac a MacBook Air or a MacBook Pro - when updating to Sequoia 15.3 you lose an external monitor capability to run dual monitors. This seems to have happened to thousands upon thousands of people.

"After Sequoia 15.3 update, external monitor is not recognised by my MacBook Air: [...]Tried various approaches and now see that others have had a similar problem.[...]"

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Question is: "Just how many people have actually reported this to Apple?"

Report this as an Update Bug to Apple:

Do your Part: Inform Apple of your feedback of this issue. Include how you’ve troubleshot this, and your results. Apple wont get back to you directly, but the more feedback they receive from its users, the more likely they will know what bug issues exist, and what bug fixes to include future macOS versions to come. Apple will know nothing of your incident, if you don't report it to them.

1. Go Here: Feedback - macOS - Apple
2. Select: "Bug Report" for the "Feedback Type"
3. Select: "Software/Firmware Update" for the "Feedback Area"
4. Proceed from there as necessary

The same thing has happened to me, I had my computer set on automatic updates and when it updated to sequoia 15.3 it took the ability for any dual monitors. I always had an extra monitor when I did work. This has been very hard because I’m a graphic designer and now I can only use one monitor. Apple needs to fix this right away. This is terrible. Note I tested the monitor. The monitor works fine on an older iMac running Catalina. It no longer works though on Sequoia 15.3.

Rcaqua Said:

"After Sequoia 15.3 update, external monitor is not recognised by my MacBook Air: Using a Macbook Air (M1, 16 GB Ram, 2TB HD, I upgraded to 15.3 yesterday and today I can no longer use the external monitor which is connected via HDMI. Tried various approaches and now see that others have had a similar problem. Is there a fix for this? Thanks for your assistance! best, rene"

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Verify if this is Seen by the Mac:

See if the items are even seen: 

1. Hold Down: the Option key
2. Click: the Apple menu
3. Select:: About this Mac...
4. Click: System Information... button
5. Select: Graphics/Display (on the left of screen)
6. Look For: this screen in the list

Having the same issue. My monitors worked fine 30 mins ago, laptop updated to 15.3, now I can't get them to work. It just says no single and they are being detected. Tried all the basically display troubleshooting methods.

Similar issue for me. I recently upgraded to a MacBook Pro M4 Pro Chip and had been running my external monitor (Odyssey G95C) flawlessly for weeks at 5120 x 1440 at 240hz resolution (with the MacBook lid open). After updating to Sequoia 15.3, this no longer works and whilst it recognises the monitor, it just shows a black screen. If I close the MacBook lid, it does work at that resolution and refresh rate, but not all the time.

It does work at 5120 x 1440 if I change the monitor to a 120hz refresh rate (with MacBook lid open), but this is incredibly frustrating the old settings now don't work at all. That was one of the major reasons for upgrading to this model! Even my 2017 MacBook Pro 13" Core i5 runs the monitor at 5120 x 1440 @ 240hz refresh (albeit using an eGPU via Thunderbolt)...

I've submitted feedback to Apple (thanks for the link)

Hello I’ve actually experienced this issue with some of the Mac’s at my university. We work with Extron systems and VIA Kramers. I’ve noticed with some of the MACS, the USB-C connection flashes in and out and doesn’t matter which resolution I switch it too. Also for some reason sequoia has got rid of 1920X1080. That’s what our systems are set to which is the standard. Also with the VIA go the update has not been to mirror the screen properly. What’s peculiar is that it works fine with some Mac’s that use sequoia, but it’s not a guarantee. Would love if someone could reach out. Or comment if they’ve had similar issues.

Unplug the monitor from wall, wait two minutes and reconnect and test.

Unplugging for several minutes did not help me. Thanks for the suggestion.

It's the same here. All I did was unplug the power cord from the monitor while leaving everything else plugged in. When I plugged the power cord back in, it worked.