Level 1 (4 points)

Command F2 for target display not working, any idea why?

Hi everyone, I am trying to use my iMac mi-2011 27" (macOS High Sierra 10.13.6) as an secondary monitor, with a thunderbolt 2 cable, my macOS version is BigSur 11.7.11 (MacBook Pro mi-2014), but command F2, working yesterday Nov. 4th 2026, is not working today Nov. 5th 2026.

No update between. No changes : I left the computers on, I disabled the Internet (Ethernet disconnected) before I stopped working, no wifi.

Any idea why?

PS: there was the same topic before but other configuration. And in my case, the apparently good answer is just… false. https://discussions.apple.com/thread/253348806?login=true&sortBy=rank

Posted on Nov 5, 2026 5:12 AM

2 replies

WheelieNick

Level 9 (74,110 points)

Nov 5, 2026 6:15 AM in response to arteange

Your MacBook Pro is running macOS Big Sur (11.7.11). Apple's official requirements state that the Mac acting as the video source (your MacBook Pro) cannot be running macOS Catalina, Big Sur, or newer. Target Display Mode requires the source Mac to run macOS High Sierra (10.13) or earlier.

But I have no idea why it was working before.. have you tried a restart to see if the issues persist?

den.thed

Level 10 (99,154 points)

Nov 5, 2026 7:03 AM in response to arteange

Sounds like that setup was Screen Sharing over the Ethernet connection instead of using Target Display Mode.

see > Share the screen of another Mac

Originally posted at discussions.apple.com/thread/256389193