I had a few issues with GNOME Music, so I downloaded the code and played around with it this weekend. First I changed my music directory from the hard-coded default value to a custom one, then I attempted to work around a Tracker/GStreamer bug that was causing all of my songs to show up as their own album.
I used GNOME Builder in this video. You can install it from your distribution's repositories, or download the Flatpak here: https://wiki.gnome.org/Apps/Builder
Here's the homepage for GNOME Music: https://wiki.gnome.org/Apps/Music
And here's GNOME Music's source code: https://gitlab.gnome.org/GNOME/gnome-music