You’d create a ZFS pool for your shares, then a TrueNAS VM which serves your ZFS pool as NAS. Then setup your Jellyfin VM using your NAS as storage for your libraries. Ends up looking like this: x0.at/Gbqm.png

Your media is accessible via the network from any device because they’re SMB shares, and it works just fine in Jellyfin. If you only create a ZFS pool for Jellyfin, your media can then only be accessed through Jellyfin. It limits your future options.