Not quite sure I understood entire post well but still looks like it is called org.gnome.FeedReader. Therefore please take a look if flatpak uninstall --delete-data org.gnome.FeedReader helps. Probably related link (current idea of mine) is mentioned here: How to install fractal next - #4 by Quarnero. As first step, to find/confirm both related applications please execute:
$ flatpak list
$ flatpak info org.gnome.FeedReader
All commands related link: https://docs.flatpak.org/en/latest/flatpak-command-reference.html.
For CLI on how to install & run please see here: https://flathub.org/apps/details/me.hyliu.fluentreader.