+1 on talking to the CAD software vendors. Very important.
Beyond that, the CAD answer used to be a 27-inch iMac with an optional i9 processor and uprated video hardware. No more. Apple in their wisdom have seen fit to discontinue 27-inch iMacs.
IHMO you best Mac option for Pro CAD use today is a Mac Studio:
Mac Studio - Apple
It has plenty of ports, comes with 32GB RAM (Should be plenty) and you can pair it with a monitor size/model of your choice. It also supports multiple external monitors. The 24-inch iMac has limited ports and supports only one external monitor.
⚠️ If you go Mac, remember: The storage and RAM you buy today will be your "forever" RAM and storage. Not even the gods on Mount Cupertino can change those after the computer leaves the assembly line.
Purchase NOW what you think you will need in three years.
If future expansion is important to you, current Macs no longer offer that luxury.