Target Display mode

Hi,

• All iMac models introduced in 2011, 2012, 2013, and mid 2014: Use a Thunderbolt cable to connect your iMac to a Thunderbolt or Thunderbolt 2 port on the other Mac. If the other Mac uses Thunderbolt 3, you can use the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter with your cable.

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.

I presume that is so?

I had similar problem - CMD F2 was doing absolutely nothing.

I solved it by resetting SMC on the iMac - do do this, shut down, remove power cord for 15 secs, plug power cord back in, wait 5 secs and then switch on.

I have iMac late 2012 with latest Catalina and 2020 MBP

However, annoyingly, I can't get it to work with my Dell XPS which is giving a Thunderbolt compatibility warning message - and it's the XPS I really want to use it for!