While debugging problems with a flatpak application, I wondered whether there is a way to manually download the current version (or another specific version) of a flatpak package to filesystem, other than installing it. Ideally, I’d like just a snapshot, like you would download a .deb file for Debian/Ubuntu or .rpm file for Fedora/Suse.
I am aware of How to download software with all its dependencies offline in a direct and easy way, however that doesn’t work for me:
$ flatpak create-usb /tmp/flatpak-test-for-signal org.signal.Signal
error: Remote ‘flathub’ does not have a collection ID set, which is required for P2P distribution of ‘app/org.signal.Signal/x86_64/stable’.
I have no clue what that means.