Target Display Mode Not Working - MBP 2020 <-> iMac 21.5 late 2012

I have an iMac 21.5 late 2012 (High Sierra) that I want to use as a second display for my MacBook Pro 13 early 2020. The MBP has Big Sur and target display mode is not working. I have tried it with another MBP early 2020, but with Catalina and that didn't work as well. I also used a MacBook Air 2018 that has Mojave and that worked well.

The cables I used is the Thunderbolt 2 cable and the TBT 3 to TBT 2 adapter but seeing as it worked with the MacBook Air, I doubt it's the cables.

So does TDP not work in Catalina onwards? Or am I missing something?

Any help would be great! Thanks :D