Greg, thank you for getting back to me so quickly with your suggestions! I worked through each one of them but sadly none of them bore fruit. I never was able to make it past the Virtual Assistant with MS Support. The NIRSoft Utility was able to show me my Product Key, but I was not able to insert that into the new installation for activation. And as for the Microsoft Store Order History, that was one of the first places I looked earlier today (as well as the confirmation email from the day of purchase), and it is as you described it: a keyless Digital License associated with the Account (or as I have most painfully learned, one specific Device linked to my Account).
I did some further reading, and tried using the slui 04 command while offline to initiate the Telephone Activation process, but it just produced an error msg saying I needed to connect to the internet to Activate Windows. I also dug a little deeper on the various slmgr commands and may have succeeded in reinstalling the license files on the old Windows VM (maybe?) because after that the old machine began appearing on the Devices page again. But when I booted up the new VM again and tried to Activate, the licensed VM would not come up as an option that I could use to Activate.
Finally, I tried using Reset Windows in the Recovery section of System Settings to reinstall the old version Windows in its original VM. That seems to have been successful in that it retained its Activation. I'm not sure if that install method is a clean install or if it's just reinstalling over top of the old one (like an upgrade) or if its something in between, but it is running much faster now. However, I'm still concerned about the portability of my Retail license. Later this fall I am planning to upgrade to a Mac Mini with an M1 chip for home machine, and that will involve another reinstall of Windows.
I must admit I am somewhat surprised and disappointed that Microsoft Support was so inaccessible on this issue. I understand there must be a gazillion Windows users out there clamoring for software support, but I would think assisting users to get Windows installed and Activated would be a very high priority. I think I may be sticking to purchasing boxed versions of Windows with Product Keys instead of online virtual Digital Licenses from now on.
But I do appreciate your help with this problem! Thank you for taking the time to look into this issue for me, and for pointing me in a few good directions in my troubleshooting.