Target display not working
I have a new iMac (Retina 5K, 27-inch, 2020) running Catalina 10.15.7.
I also have an old iMac (27-inch, Mid 2011) running High Sierra 10.13.6.
I want to use the old iMac as a second monitor. The 2 iMacs are connected with a Thunderbolt cable. When I press Command-F2 on the old keyboard, nothing happens.
I tried restating both iMacs and unplugging and replugging the Thunderbolt cable. I also tried login out and pressing Command-F2.
I am using the original keyboard on the old iMac. The Thunderbolt cable is from the Apple store. What is wrong? Why does nothing happen when I press Command-F2?
iMac Line (2012 and Later)