If you already have the correct version of the flatpak installed, you can try flatpak build-bundle.
flatpak build-bundle LOCATION FILENAME NAME where
LOCATIONis the path of the repo on disk. Runflatpak info -l org.kde.arianna, and copy the part before/appFILENAMEis the output file name, preferably.flatpak. Eg:arianna.flatpakNAMEis the name of the app, hereorg.kde.arianna
The generated file can be installed with a double-click, or with flatpak install <file>
This is the equivalent of an Android .apk. It contains the app but depends on a runtime. If you want to install it in a few years, odds are the runtime will no longer be available. You can backup the runtime the same way with the --runtime option.
flatpak build-bundle --runtime LOCATION FILENAME NAME where
LOCATIONsame as earlierFILENAMEegarianna-runtime.flatpakNAMEis the name of the runtime, which you can get withflatpak info --show-runtime org.kde.arianna
This takes a while, for some reason. Maybe it's compressing stuff?
The runtime is installed the same way as the app: double click or flatpak install.
Note: I only did this once, and not specifically on Arianna. Hope it works.
Like having superhuman levels of cholesterol