Lots of x86 machines are hitting the curb this week because they won’t run Windows 10. One of those with a Linux distro installed will do what you want. Follow the directions in Jellyfin’s documentation and you should be good. Adding your devices to a Tailscale network is the fastest way to be able to access your content outside of your home network. FireTV has a Jellyfin client and can also be added to Tailscale.