I might have some good news for you. I believe I told you that I was able to get Musicmatch 7.2 to work on my Windows 10 computer. The watchfolders would not work, but everything else did. It was a little buggy and would sometimes stop and had to be restarted.
Microsoft put out a Windows 10 update for 2019. I updated my computer with the new update. After the update was finished, I was able to install Musicmatch 10.00.2058. I couldn't believe it worked. It is a little buggy at times. The watchfolders work to some extent. I have a very large music collection, so when I elect to check the watchfolders, MM would stop working. For some reason, Musicmatch won't let me drag and drop my music files into the library. (I could with 7.2) I have had to use the the "add tracks" feature to get most of my music back into Musicmatch.
I think the reason Musicmatch 10.00.2058 works is because there is no Px.dll file which was the reason I couldn't get other MM10 versions to work.
If I add new music to my watchfolders, Musicmatch does add those to the library. It is my original music that Musicmatch seems to have a hard time accepting.
The player works when I add songs to the playlist. I can also retag songs which is one of the major reasons I keep using Musicmatch.
Not sure what the new Microsoft update had to do with letting Musicmatch 10 install, but I was thrilled to have MM10 back. Hope this information helps you to get it working for you too!