Does Jellyfin have Remote Access?

[TheDreadPirate]

Does your ISP use CGNAT?

[gizmomelb]

it's not the safest but having port forwarding on your router to your server with jellyfin should just work (make sure your jellyfin server is set to a static ip on your lan).

check your router that it is port forwarding port 8096 (TCP and UDP worked for me when I just tried it) to the IP of the jellyfin server on your LAN.
also make sure the forwarding rule is set to enabled and uses the correct interface (ETH - not VDSL or others) or it won't work.
try to connect to your server using a mobile device to test if it works (diable wifi on the mobile device so it's using 4G/5G)
also it helps if you have a static WAN IP from your ISP - or you'll need to set up some dynamic DNS so external devices can still connect to you when your ISP changes your WAN IP.