I would recommend looking at 2016-era Xeon E5 processor and appropriate motherboard with plenty of memory. Some of these Xeons had up to 22 cores. I got Xeon E5-2690 with 14 cores and 28 threads for a whopping 50.00 on ebay. They can be had for pennies on the dollar and you can do a lot with them. I wouldn’t go older than 2016 because those tended to have a lot of power draw and heat. Then I would use ECC RAM if you intend to use as a NAS.
If I were you I would not host Jellyfin publicly. Please use a VPN like Tailscale or ZeroTier. If you feel particularly intrepid you could try using Nebula for your VPN platform which is completely open source and free. I am in the midst of using Nebula to build out my own software-defined overlay network.
I drew the same conclusion initially from the headline. I was like … Wut!?