Follow these simple steps to start using Flatpak
To install Flatpak, enable the ~amd64 keyword for sys-apps/flatpak, acct-user/flatpak and acct-group/flatpak:
# echo -e 'sys-apps/flatpak ~amd64\nacct-user/flatpak ~amd64\nacct-group/flatpak ~amd64\ndev-util/ostree ~amd64' >> /etc/portage/package.accept_keywords/flatpak
Then, install Flatpak:
# emerge sys-apps/flatpak
$ flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
$ flatpak remote-add --if-not-exists ramatak https://download.ramatak.com/ramatak.flatpakrepo
Note: graphical installation of Flatpak apps may not be possible with Gentoo.
To complete setup, return to the download page, and follow the instructions.!