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User profile for user: Clubnev
Clubnev Author
User level: Level 1
29 points

My Apple desktop monitor isn't recognized as an external monitor with my MacBook Pro

I have a MacBook Pro running Big Sur 11.2.3. I have been using my old Apple desktop as an external monitor (running Catalina version 10.15.7; it won't support Big Sur) for a few months with the last Big Sur update (I think 11.2.2 but not sure). Yesterday, out of the blue, my MacBook Pro quit recognizing my Mack desktop as an external monitor. I just updated Big Sur to 11.2.3 hoping that would fix the problem. It didn't. They are connected with a USB to USB C adapter.


There are alot of similar problems with Big Garbage Sur with external monitors but no questions I found that specifically are for an Apple desktop as an external monitor.


Any solutions? If I can't use my laptop with an external monitor, I might as well throw it out the window and go back to Windows. SO DISAPPOINTED IN APPLE LATELY.


Thanks

MacBook

Posted on Mar 14, 2021 3:05 PM

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User profile for user: Grant Bennet-Alder
Grant Bennet-Alder
User level: Level 10
133,861 points

Posted on Mar 14, 2021 4:50 PM

"Target display mode requires macOS High Sierra or earlier on the iMac used as the external display. It does not work with macOS Mojave or later.."


from:

Use your iMac as a display with target display mode - Apple Support


.

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User profile for user: Clubnev
Clubnev Author
User level: Level 1
29 points

Mar 14, 2021 7:55 PM in response to Grant Bennet-Alder

These monitor problems started with Big Sur from most of the forums I read. My iMac has been working fine as a monitor for a couple of years. Then I installed the Big Sur update on the Mac Pro and bam. No more. My husband's is still working - Catalina on the iMac and Big Sur on his 2014 Mac Air. It's connected differently since it doesn't have USB-C. I will call Apple Business tomorrow and see what words of wisdom they have to offer. If they have anything useful to offer, I'll post.

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User profile for user: Grant Bennet-Alder
Grant Bennet-Alder
User level: Level 10
133,861 points

Mar 15, 2021 8:52 AM in response to Clubnev

Half of those other users may be using outdated equipment (such as Macs issued in 2020 or later), inappropriate cables, or initiating Target Display Mode incorrectly.


Rely on what you can read from official Apple articles, like the one posted above. You must follow ALL the procedures faithfully.


¿Is your iMac from the supported group of model years? Running High Sierra or older?


¿Is you MacBook Pro from 2019 or earlier?


¿Are you using the supported cables {Mini display port (if both support only that), otherwise genuine ThunderBolt cables and possibly a Thunderbolt-3 <-> ThunderBolt-2 adapter?


NB>> NO USB-C cables are supported in any configuration. If you got that to work, you just got lucky, and later versions of Big Sur removed that luck.

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User profile for user: Clubnev
Clubnev Author
User level: Level 1
29 points

Mar 15, 2021 11:11 AM in response to PaulBraun

Apple Business set all of this up. They sold me the cables, - a thunderbolt for the iMac to a USB-C connection for the MacPro. My MacPro only has a USB-C connection. They walked me through the set up and it has been working great for just shy of a couple of years. And it has been working with Big Sur (and whatever came before it, I can't remember) on the Pro and Mojave & Catalina on the iMac. Now it isn't. There's complaints all over the web - not specifically with an Apple iMac but with ANY monitor, even some Apple displays that are new. So I suspect that's some kind of a bug.


I am able to connect an LG monitor - HDMI to USB-C. Works great. Seems very odd that I can use a third party monitor but I can't use an Apple product. So I will call Apple Business later and see what they say. And I'll ask about the article that Grant posted. If they give me anything relevant, I'll post.

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My Apple desktop monitor isn't recognized as an external monitor with my MacBook Pro

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