I followed these instructions but they just install the server side of jellyfin which I don't need. I tried the flatpack option but the software GUI that Fedora KDE comes with seems to have no idea what to do with the flatpakref file
Try searching for the Flatpak directly in the Software GUI ("Discover"), it should come up in there.
Additionally, for Flatpaks I'd recommend installing the extension "Flatline" which will make it so that instead of it downloading flatpakref files, it'll just launch Discover automatically.