Follow these simple steps to start using Flatpak
Flatpak can be installed from GNU Guix's default repositories. Run the following in a terminal:
$ guix install flatpak
Flathub is the best place to get Flatpak apps. To enable it, run:
$ flatpak --user remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
To complete setup, restart your system. Now all you have to do is install some apps!
Note: graphical installation of Flatpak apps may not be possible with GNU Guix.