Follow these simple steps to start using Flatpak
A flatpak package is available in Debian Buster and newer. To install it, run the following as root:
# apt install flatpak
For Debian Jessie and Stretch, a flatpak package is available in the official backports repository.
If you are running GNOME, it is also a good idea to install the Flatpak plugin for GNOME Software. To do this, run:
# apt install gnome-software-plugin-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
To complete setup, return to the download page, and follow the instructions.!