Using 2011 iMac As External Monitor for 2019 iMac

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Using 2011 iMac As External Monitor for 2019 iMac

I've read a ton on the setup described in the subject line, and am just looking for confirmation that it can't be done, at least as my newer iMac is currently set up.

The 2011 iMac is running High Sierra 10.13.6

The 2019 iMac is running Big Sur 11.5.2

They are connected using an Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter.

From what I have read, the reason Target Display Mode will not work, (and thus, I cannot use the older iMac as an external monitor for the newer iMac), is that the OS on the newer iMac is more recent than Catalina. Is this correct?

The odd thing about this is that I was using the older iMac as an external monitor for the MBP my former company issued me, and know that I was running Big Sur on that computer, before I turned it in when I left the company.

Thanks for the confirmation, bummer that I can't use the 2011 iMac anymore.

iMac 21.5″, macOS 10.13

Posted on Oct 27, 2021 7:17 AM

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Answer 1

Allan Jones

Level 9

78,224 points

Oct 27, 2021 7:29 AM in response to jmdaniel

The video source computer, in your case the 2019 iMac, cannot have a higher macOS version than 10.15 Catalina.

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

Apple began deprecation of Target Display Mode in late 2014 and threw the last shovel of dirt in its face in Feb 2020. Starving internet journalists, lacking editorial help or kindergarten research skills, rushed to take advantage of the work-from-home movement and published a lot of post-processed horse feed about Target Display Mode. They attributed feats to TDM that never existed.

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Using 2011 iMac As External Monitor for 2019 iMac

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