I’ve downloaded bunch of Jellyfin apps from flathub and AUR. There’s nothing like in the Windows where you will be directed in a browser and let’s you host from it.
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Did you start/enable the
jellyfin.service systemd unit, as mentioned in the Arch Wiki?
In the same Wiki page it is mentioned that in order to configure Jellyfin, you have to browse to http://localhost:8096/ (after enabling the systemd unit).