iMac 2020 with iMac Late 2014 as 2nd display

I bought a cable and adapter: Thunderbolt to Thunderbolt cable and a Thunderbolt to USB-C Adapter. The connection point where the adapter and cable come together is warm to the touch but the 2nd display is not working.

I have an iMac 2020 running macOS Monterey v12.0.1 (27") and I'm trying to use my old iMac Late 2014 running macOS Sierra v10.12.6.

Is it possible I have a cable problem? It seems straightforward to hit Cmd-F2 and I've tried re-starting both computers, reconnecting, as well as logging out of the display computer and hitting Cmd-F2 and it's still not working. I'm upset that I spent $84 and I can't get the setup to work!

Both computers have Apple original keyboards and trackpads. Help!