Computer purchase

Hi,

thank you very much. 

You are pretty much stuck with the outgoing Intel-powered Macs because the current M1 Apple silicon Macs neither can be ordered with more than 16 GB total of RAM nor is available with a discrete GPU at all. (After Effects officially requires 16 GB or more installed RAM in order to run properly.)

Among the outgoing Intel-powered Mac desktops, the only ones that are suitable for this besides the massively expensive iMac Pro and the Mac Pro are the higher-end 27" iMacs.

If these higher-end Macs are on their way out of production, I would wait for new, more powerful Apple-silicon CPUs to be shipped to resellers before you make your decision.

I don't know if Mac is discussed much, but a link of information

This includes 2 recommendation links from Puget Systems... copied from Peru Bob
https://community.adobe.com/t5/video-hardware/premiere-pro-hardware-articles-to-read-before-you-buy-or-build/m-p/11557686