Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
I understand everything you said in your post. When I was notified in October 2017 that Office 2011 would no longer be supported, I acquired a copy of Office 2016.
I had created a complex application in Excel 2011 (lots of macros). When I started it up in Excel 2016, It would not run properly. At this point, I don't remember all the things that would not run, but do remember concluding that I could not afford the time or effort to modify the application. It wasn't just a case of tweaking the code for Excel 2016. Some commands I had used were no longer valid in 2016 and I would have had to redesign a lot of code.
I reverted back to Office 2011.
I knew that, at some point, Apple would no longer allow 32 bit code, and at that point I would have to do whatever was necessary to get my application to run in Excel 2016 (or maybe now Excel 2019).
The best thing would be that I will start up my application and everything will work properly. The worst thing would be that I will have to do a complete redesign of the application. Having experienced Microsoft upgrades to their products many times in the past, I hope it will be the former, but I am quite confident I will have to do the latter.