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I currently have:

  • 2019 MBP on MacOS 10.14.6
  • 2012 iMAC on MacOS 10.14.6 (thunderbolt 2)

I am connecting them to each other using a Thunderbolt 2 to Thunderbolt 3 adapter, both of which are brand new.

I was able to trigger target display mode ONCE. Then cmd + F2 stopped responding entirely. Things I've tried:

  • reset the PRAM/NVRAM on both devices
  • cmd + F2 + fn
  • every combination of the ports on each end
  • booted the iMAC in safe mode (can't do it on the MBP; it's a work laptop)
  • tried initiating TDM by connecting iMAC to MBP 2014, still no dice on cmd + F2

I've perused all the Apple support pages and similar stackexchange questions to no avail and now I'm at my wit's end. Did anybody face something similar and was able to resolve?

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  • do you have a Retina display. According to one source Target display mode not available on iMacs with retina displays.
    – Natsfan
    Jun 10, 2020 at 21:34

2 Answers 2

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Did you use a 'Thunderbolt' or 'Thunderbolt 2' cable to connect the two macs? Also judging by your description the iMac has Mojave installed whereas TDM would work only on an iMac with High Sierra or below. For reference please follow this official Apple article: https://support.apple.com/en-us/HT204592

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  • ?? The Apple tech who talked about TDM on my 2019 MBP with Big Sur is ignorant?
    – WGroleau
    Mar 19, 2021 at 16:47
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I recall that you have to be logged out on the target iMac for target display mode to work. I recall seeing this in a YouTube video but not where, and it is pretty obscure so I doubt I'll find it again. otherwise I'd link to it. Apparently once logged in something interferes with the Command+F2 keyboard macro.

Also, keep in mind this is a feature Apple no longer officially supports. They stopped supporting this feature some time ago and so any software that was required to make this work may no longer be in place. The tech support people at Apple will no doubt be helpful geeky types and if you contact them then they will do their best to make this work for you but that's not going to restore whatever old software was in place that made this work a decade or so ago.

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