At work I continue to run two of these Unix workstations, one is AIX running 6.3L and the other is UP UX 11.11i (but this system is mothballed).
Ford continued to support Unix until 2013 or 2014 and as a result we were continuing to use our workstation that cost well over $25k on with supported CAD to boot. Once ford dropped Unix it all moved to Windows.
I maintain the systems to this day and there are still some customers who use the Unix programs (I-DEAS formerly from SCRC) for their CAD but it's basically dead.
One has to remember these systems had 8/16 GB Ram in 2003-2005 when Windows systems capped at 3 or 4 GB Depending on the application and this is why Unix was favored, but monolithic enterprise slowness caused Unix support to drag on another full 10 years.
CAD Vendors have all dropped Unix support save for a couple who maintain SOME: Dassault CATIA and related tools support IBM AIX and Power 8/9 platforms, but only for the back end. Some tools support Linux for the back end but for front end nothing is supported. OSX has some support, namely with Autocad and Draftsight (Autocad clone) but most CAD support for OSX are for viewers only not full blown CAD tools. I would hope that OSX carries the torch for Unix Workstation performance but Apple's insistence on changing and dropping older hardware, architectures, and application lock in seem to make CAD vendors think twice about spending millions to port their code over to OSX - even though some of their code bases began and are still maintained as Unix based.
Lastly, Linux support for most CAD tools is all but dead on the GUI side, only back end processing/FEA is Linux supported. The last vendor dropped Linux support for GUI CAD tools in 2018 or so. Too many splinter distributions of Linux to maintain therefore they're out.