Since pfsense is a firewall product and not a file server, I don't think you're going to find any kind of solution for this. You really don't want the device that's protecting your internal network(s) to be a file server anyway. If your firewall were to get compromised somehow, your attached storage devices would most likely be targeted as well.
How about getting a dedicated NAS box, personal cloud storage device, or network storage adapter? These devices would sit inside your network, protected from outside access, behind the firewall. Do you have a PC on your network that's always on? That could act as a network disk server.
https://www.amazon.com/TerraMaster-Transcoding-Personal-Storage-Diskless/dp/B07PWDTBJ6
https://www.amazon.com/KwiltGo-Personal-Cloud-Storage-Device/dp/B07SJHSSMP
https://www.amazon.com/Synology-DS120j-DiskStation-Diskless-512MB/dp/B07ZKSLVT5
https://www.amazon.com/Usr-Ushare-Mini-NAS-Adapter/dp/B0050JRXVU/
You could even get one of the less expensive wifi routers that has USB ports on them, set it to serve no network functions, but to instead host your hard drives on the network.
https://www.amazon.com/TP-Link-AC1750-Smart-WiFi-Router/dp/B079JD7F7G/
Hope that helps.
Jeff