Hi Paul,
quite a long time ago I had the same problem. I followed this instructions and it worked for me:
In fact I have several games in the UWP store (even on XBox 1 Store) which use this hack.
It is not a matter of using or not using ‘song’ (or other functions). As long as the DLL includes them, the stupid UWP store will complain. So, in these instructions you end up “emptying” the DLL in order to pass certification (extremely ugly hack)
If you install a new MonoGame version, you have to do the whole process again as the new installation will probably overwrite the modified DLL.
Now for a cleaner/definitive fix… the problem resides in SharpDX. The SharpDX dll 4.1 ( Latest sharpdx fails windows store certification! (4.0.1) · Issue #939 · sharpdx/SharpDX · GitHub ) has been fixed but not available still as stable version. The MG team will include the fix as soon as the SDX 4.1 goes stable.
You could try to compile MG with the 4.1 pre-release version, or modify the SharpDX 4.0.1 stable to include the UWP fix and then compile MG with it, or go with the ugly hack. That’s all I can think of.