This flatpak package bundles the latest stable and the unstable
versions of LilyPond.
When you launch it the first time, Frescobaldi will detect only the stable
version, installed in /app/bin (which has higher priority in the PATH
environment variable).
In order to use the unstable version of LilyPond, you must manually add
the path /app/dev/bin/lilypond in LilyPond Preferences.
If you want to use a particular version of LilyPond which is
not bundled in the flatpak, you should download the right binary
for your platform from lilypond.org, unpack it in a folder
(e.g. ~/.local/lilypond) and then grant access to that
folder using either Flatseal
or flatpak command line.
NOTE: self-compiled LilyPond will likely not work.
The beta branch of this repository will be used to test the latest unreleased Frescobaldi (if there's anything interesting to try) and/or a peculiar LilyPond installation (new features or dependencies).