It was pointed out to me today that I could use my late 2012 iMac 27" as a display for my late 2019 MBP 16". But I will need to buy a Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter. I never had a use for this feature as my last MBP was a early 2011 model. Below are the technical requirements & procedures on how to enable this feature. Target Display Mode isn’t supported on iMac models with Retina display. Only these iMacs support Target Display Mode. iMac (27-inch, Late 2009), iMac (27-inch, Mid 2010), and iMac (Mid 2011 to Mid 2014) You can view the desktop of your Mac on the display of some iMac models using Target Display Mode. In some cases, you can also use Target Display Mode to play the sound from your Mac (called the primary Mac) on the speakers of the external iMac. For example, if you have a MacBook Pro you could use an iMac as the display and for playing audio. https://support.apple.com/en-ph/guide/mac-help/mh30822/mac Use an iMac with Thunderbolt as an external display If you have an iMac with Thunderbolt, any other Mac with Thunderbolt can use it as a display. The iMac will play both the video and audio from the other Mac. Connect the Thunderbolt cable to the Thunderbolt ports on each Mac. Make sure both Mac computers are turned on and awake. Press Command-F2 on the keyboard of the external display iMac. If you want the iMac to play audio as well as video from the primary Mac, go to the primary Mac, choose Apple menu > System Preferences, click Sound, then click Output. Select the Mac in the list of devices.