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User profile for user: Chunga
Chunga Author
User level: Level 1
8 points

How to use an iMac as an external monitor

I'm trying to figure out, unsuccessfully, how to use one of two iMacs I have and external monitor for my MacBook Pro. I've connected them with a thunderbolt to thunderbolt cable. My MacBook Pro is a Mid-2015 15" running Big Sur 11.4 ... and I have 2 iMacs, one is a late 2009 27" running High Sierra 10.13.6 and the other is a Late 2012 27" running Mojave 10.14.6


Ive tried restarting, keeping the iMac on the login screen, having the MacBook logged in and holding down command F2 on the keyboard connected to either iMac... nothing seems to work, I can't get either into target display mode or act as an external monitor.


Does anyone have any ideas? What am I missing? Thanks!!!

iMac, macOS 10.12

Posted on Jun 19, 2021 11:28 AM

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User profile for user: Jack-19
Jack-19
User level: Level 8
45,872 points

Jun 19, 2021 11:32 AM in response to Chunga

Hi Chunga,


Welcome to Apple Support Communities.


Unfortunately, you cannot use Target Display Mode on your MacBook Pro since it is running macOS Big Sur, and that is not compatible.


You cannot use it on your 2012 iMac since it is running macOS Mojave. In order to use this Mac as a Target Mac, it must be running macOS High Sierra or earlier.


One configuration that may work is using the 2012 iMac as the output (source) Mac, and the 2009 as the Target Mac. This may work.


Resources:

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


-Jack

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How to use an iMac as an external monitor

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