Gentoo

Install Flatpak
To install Flatpak on Gentoo, open the Terminal app and run:

emerge --ask --verbose sys-apps/flatpak
Add the Flathub repository
Flathub is the best place to get Flatpak apps. To enable it, run:

flatpak remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo
Restart
To complete setup, restart your system. Now all you have to do is install apps!

Note: graphical installation of Flatpak apps may not be possible with Gentoo.

Install Flatpak