Using 2013 iMac running Catalina as external display for a 2021 MacBook Pro (M1Max) running Monterey

Today, I received my new MBP which substitutes my 2017 MBP.

I had my old MBP connected with the Apple Thunderbolt 3 to Thunderbolt 2 and a Thunderbolt 2 cable to the 2013 iMac. With Command + F2 on the iMac, I was able to extend my MBP to the iMac display.

I expected that this would also work with the new 2021 MBP, but it does not … Any clue why?

I found videos using the M1 Air to connect to an older iMac and using that display to extend the desktop. Hence, I do not believe that the M1Max would limit it in my 2021 MBP …

Anybody else with such an issue?

The 2013 27” iMac has a nice display which I would like to use with the 2021 MBP …