I pursued this as an experiment and it turned into quite a saga, so I thought I'd share for the benefit of all:
After MUCH research and HOURS of watching YouTube videos and reading LOTS of articles, I found that there are totally legitimate sites that do sell totally authentic and legitimate product keys for older versions of Office. I purchased Office 2016 key for about $22 and it was easy and simple... Until Microsoft got involved. So I entered the key on office.com/setup and it validated and confirmed that it was legitimate. It allowed me to download the installer (office.exe), however, this file would not work no matter what. I tried everything (hours of troubleshooting), and after no success, I went through a gauntlet of ridiculousness with MS support. This got handed up to second-level support.
Bottom Line: It came out that the problem wasn't on my end, or my computer, or with the key or anything, but that the file stored on the MS server was corrupted and wouldn't work when downloaded. This support person had to go to some random third-party vendor who had a complete image file of Office 2016, download it, and help me extract it to get it installed. The level 2 support was actually good, but it was a character-building experience getting to that point.
The strong implication is that there are legitimate new and used copies of retail office software available for purchase, but MS doesn't want you using them because they would prefer you pay for a monthly subscription, so they leave installer files for these older versions that don't work laying around on their servers.
Anyway, it's working now, and so is my syncing with outlook.com... so all is now almost as it was in this part of the universe... whew!!
Except, now Outlook 2016 will not store/save my desired view (ie no folder pane in a dedicated calendar window, while I have a folder pane in my primary email folders/inbox window). I can't figure out how to get it to retain the view settings I give it. So gotta do more digging... unless someone here has seen this one?
Anyway, thank you for all the ideas/assistance as always Diane and company. This group is awesome!