Mr Allen,
(BTW, I don't work for JRiver, this is just my opinion)
A) OS updates break things. It's a fact of our computing world. It's not fun for you that this happened; sorry for your luck. This is one reason I stay away from early OS upgrades on my systems.
B) I've offered you a free solution to your problem. Sure, it's not what you're used to, and it will require a little bit of setup effort. Things change. People adapt. Life moves on.
On the other hand, MC21 has some exciting new features that you might enjoy. Video is the big one. Video support is VASTLY improved in MC21. I'm LOVING video support in MC now. If you have a video collection, it might be worth it to upgrade. ...and as Jim said, there's a 30 day free trial. I've seen some weird issues with the trial period on systems that already have MC20 installed, but hopefully those are resolved, so you can fully test it.
So you've got some lemons on your table. Let's make some lemonade.
Brian.