A definitive fix for the Flatpak installation error: runtime/org.freedesktop.Platform/x86_64/1.6 not installed.
Fix for Flatpak Installation Error
Flatpak is a new way of distributing apps in the Linux ecosystem, and while enabling Flatpak, you may face some unwanted errors like the below:
error: runtime/org.freedesktop.Platform/x86_64/1.6 not installed
If you interrupt the process while enabling Flatpak repositories for some reason, e.g. internet connectivity loss etc., the Flatpak installation remains incomplete and may unstable your system. There is a likely chance that you may get the above error while installing any Flatpak apps after you encounter the above error.
Before trying the fix, ensure your Linux system is up to date. Make sure to install all pending updates from your official Linux distribution repository and do a clean reboot.
If you face the above error, run the below command from the terminal and reboot the computer. This command would correct any missing packages/errors and make your system usable for Flatpak.
Remember that the following command will update all your installed applications and runtimes to the latest version.
flatpak update -v
After reboot, try to perform the operation which you were trying to do. It would be resolved.
If the above command and steps do not work, then try the following in the order they mentioned below. These may or may not work because of various configurations and system states.
flatpak uninstall --unused
Then restart and try.
Let me know if this solves your error using the comment box below.