Migration of Android Songbook to new Musescore app

I am a bit confused. In a help file (I think), I read that the Premium Musescore app will be getting the features of Songbook, and that owners of Songbook will be given a free migration to Premium Musescore. However premium features will be subscription based. Kindly clarify this, and also provide a timeframe, and what we need to do in order to migrate.

Also, how does one associate .mcsz files in Android with Songbook. My email will open an attached file in Songbook, but my file manager apps do not know what to do with a .mcsz file. I would like them categorized as music files with the correct app association. Also, if I click on a .mcsz file in pCloud, nothing happens. And I have not figured out how to copy a file from pCloud to Android storage. If, from my Android device, I go to a score in musescore.com, I am given the option to open the score in the app, but it opens the score in the Musescore app, rather than giving me a choice of Songbook or Musescore.

Advice regarding either topic would be much appreciated.