* Source code is: https://gitlab.gnome.org/GNOME/rhythmbox/-/tree/master
* Ways to work on it: https://gitlab.gnome.org/GNOME/rhythmbox/-/blob/master/HACKI...
* How to build it locally: https://gitlab.gnome.org/GNOME/rhythmbox/-/blob/master/INSTA...
What GNOME projects are you looking at?