How to enable Flatpak in Kubuntu 22.04 LTS

[Schwarzer Kater]

If you want to use Flatpaks complementary to or instead of Snaps you will have to manually enable Flatpak support in Kubuntu 22.04 LTS first.

Here is a step-by-step tutorial:

Warning:
You have to enable both the Kubuntu Backports and the Kubuntu Backports Extra PPAs to get Plasma 5.27.x with plasma-discover-backend-flatpak version 5.27.x to make Flatpak management work in Discover ! (see e.g. KDE Plasma 5.27.10 available in Kubuntu Backports Extra)

Otherwise Discover will crash when plasma-discover-backend-flatpak is installed !
Managing Flatpaks in CLI works without problems in Plasma 5.24.x (e.g. with the Konsole terminal emulator).

1. open the Konsole terminal emulator from the -> Application Launcher -> System
2. enter
   a) sudo apt update && sudo apt install flatpak and your password
   b) and for Plasma 5.27.x additionally sudo apt install plasma-discover-backend-flatpak
   (this will install two things:
   a) the system's Flatpak support itself (which can be used in CLI, see flatpak --help and man flatpak) and
   b) for Plasma 5.27.x additionally the Discover support for Flatpak to find, install, update and remove Flatpaks with the Discover software center)
3. to enable the Flathub repository for Flatpaks
   EITHER in Konsole enter
   flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
   OR for Plasma 5.27.x in the -> Application Launcher -> System -> Discover software center
   -> in the left part go to Settings -> click the button at the right side [Add Flathub]
   (both will enable the Flathub repository for Flatpaks, which is currently the largest one and is supported by e.g. KDE and GNOME - you can enable other Flatpak repositories like e.g. the one from Fedora or from individual developers later on if you wish to do so)
4. restart your system or at least log out and in again
5. For Plasma 5.24.x I suggest to additionally install the Flatseal Flatpak to be able to manage the permissions of individual Flatpaks.
   If you have upgraded to KDE Plasma 5.27.x with the Kubuntu Backports and Kubuntu Backports Extra PPAs, you can install the Flatpak Permissions Settings module for System Settings instead of the Flatseal Flatpak :
   In Konsole enter sudo apt install kde-config-flatpak and your password.
6. done - you can now
   · use Flatpaks and manage them in the Konsole terminal emulator (or in Plasma 5.27.x additionally with Discover ) and
   · manage their permissions in Plasma 5.24.x with the Flatseal Flatpak or in Plasma 5.27.x with the Flatpak Permissions Settings module in
   -> Application Launcher -> Settings -> System Settings -> Applications
   (or you can manage their permissions in Konsole too, of course)

Please know that both Flatpaks and Snaps use up more space of your storage medium than programs "traditionally" installed by apt.
Flatpaks have some advantages and disadvantages that Snaps don't have and vice versa.

[Schwarzer Kater]

Rewritten because of this thread…