Flatpak is a software packaging system that makes it easy for users to install software on a variety of Linux operating systems. It's good for software developers too because it makes it easy for them to distribute their software.
If you want to install flatpak on your Ubuntu system so that you can install a variety of software packages available in flatpak format, just follow the following commands.
sudo add-apt-repository ppa:alexlarsson/flatpak sudo apt update sudo apt install flatpak
Now you will be able to install flatpak apps from the command line.
If you would like to install flatpak apps without the command line, you can install the flatpak plugin. You can install it with the following command:
sudo apt install gnome-software-plugin-flatpak
There's also a repository for flatpak applications, called flathub, that you can install like this:
flatpak remote-add --if-not-exists flathub flathub.org/repo/flathub.flatpakrepo
From: Ubuntu Quick Setup