To build and install it:
# Remove all `--user` to install system-wide
$ flatpak --user install org.flatpak.Builder
$ flatpak --user run org.flatpak.Builder \
--force-clean \
--user \ # Remove this line to install system-wide
--install \
--ccache \
builddir \
org.freedesktop.Sdk.Extension.babashka.yamlBuilding with the --sandbox flag is not supported.