Flatpak is in the universe repo - which you might not have setup on install.
Go to a terminal and run `sudo add-apt-repository universe` - if that finishes successfully, you can proceed with the setup as explained in the setup guide.
Flatpak is in the universe repo - which you might not have setup on install.
Go to a terminal and run `sudo add-apt-repository universe` - if that finishes successfully, you can proceed with the setup as explained in the setup guide.