Target Display Mode with Mid 2020 iMac

Hello all,

Does anyone know if there has been a hardware charge in the 2020 iMac which would prevent output using Target Display mode? Or, maybe the required dongles have changed?

I just got the new 2020 iMac. Previously I was using a 2019 iMac with TDM on my old 2013 iMac. TDM worked flawlessly. But since I swapped the 2019 iMac for the 2020 iMac TDM has stopped working.

I've swapped ports, rebooted both machines, and updated the 2020 iMac with no results.

I have the appropriate Apple Thunderbolt 3 Type C to Thunderbolt 2 adapter along with the Apple Thunderbolt cable per this article https://support.apple.com/en-us/HT204592

Any thoughts or solutions?