Setup the Flathub remote. Then:
flatpak install -y flathub org.flatpak.Builder
This package provides a Flatpak copy of Flatpak Builder. This is primarily meant to be used for Flathub submissions and infrastructure and as such will follow the requirements of Flathub, but it can be useful for general use as well. It also includes some other tools such as flat-manager-client and flatpak-builder-lint.
Please refer to the Flathub submission docs on how to use this to build Flatpaks for Flathub: https://docs.flathub.org/docs/for-app-authors/submission#build-and-install
The package is continuously updated and deployed from the master branch of the manifest repository. Refer to the manfiest to check the latest versions of the included components.
Please refer to the individual components for details about their respective licenses.