Warrennn

Yes, the problem is that no Ashlar products work on any version of macOS since Mojave, which is 3 years old. As far as I know, the apps are not even 64 bit, which is necessary for the most recent two Mac operating systems. Even though Ashlar has said that it will eventually support current macOS, my sense is that they are on the way out.
I have been playing with viaCAD and am impressed with it. It has the same wonderful "drawing assistant" as the Ashlar products (the developer at Ashlar left the company and went to the people who make viaCAD and took his code with him). The app is much less expensive ($200 for the version I am using) and works well on an M1 Mac using the translator Rosetta2. It is certainly adequate to do what I want. The last time I looked, Ashlar Graphite, which is much less capable than viaCAD, cost $1500. The word is that Ashlar products will henceforth only be available via subscription, which is unacceptable to me.
These products don't have the polish of Designer, but they do work well.
Again, thanks for your help.

Again, many thanks for all of your help on this. I think that the app is not intended to draw accurate 3D objects which can be rotated and transformed in other ways.
My first (physics) book was illustrated using an expensive CAD program (Vellum) which I had ,used before I retired - it cost $1500 and was the newest version of a program which had won awards for its ease of use and elegance. As a retiree I was able to get it for $700 but it is not likely to be ported anytime soon to my new Mac and I didn't want to pay an exorbitant fee to get a compatible version (my understanding is that it will be subscription-based; I don't find this to be acceptable). 
Designer is a very elegant and beautiful program and I thought that with the introduction of isometric views that I would be able to use it for 3D. Unfortunately, that was not the case. There is another program, VIaCAD, which is based upon the Vellum drawing engine and costs $200, a reasonable price for a program which would work well for my needs. It is not as pretty as Designer but it does the job and I am familiar with its user interface (almost identical to Vellum's in most important ways).
Thanks again!