late 2011 iMac as extended screen for 2020 iMac

I’m trying to connect as an extended screen, my late 2011 iMac 21.5” to my new 2020 iMac 21.5” with retina display. I had to use two adapters to connect the 2011 thunderbolt port to the USB C port on the new iMac. Whatever I try (command F2, or Preferences>Displays>Detect Displays) I can’t get the new iMac to recognize the display on the old iMac. I suspect it may not be possible to use the old screen as an extended display, ...perhaps because the new one is retina...or because of other changes. Is there a way to make this work?