Cannot connect externally when server is connected to a VPN

[meltham]

Are you able to exclude Jellyfin from your VPN?

When you enable a privacy VPN, it will enable firewall rules to block incoming traffic from other interfaces, with the exception of local network traffic to the router which is necessary for things like DHCP. But these rules can often be configured to allow other local network traffic as well (like what appears to be happening in your case).

What I suspect is happening is that your VPN rules are seeing an external IP on the port forwarded traffic and blocking it.

As TheDreadPirate mentioned, the easiest thing to do would likely be to exclude port 8096 from your privacy VPN.
If that isn't an option, it might be possible to create a custom firewall rule to allow external traffic through 8096 (overriding the VPN's rule [this is what I do, but I'm on linux]). Or you could create a reverse proxy elsewhere on your network to accept the port forwarded traffic which your Jellyfin server would then see that as internal traffic.

Thank you both for your assistance and explanations. I have managed to get around this using a reverse proxy on another device in the network, just like the way mildlyjelly suggested.

mildlyjelly - how have you managed to create a custom firewall rule to override the VPN's rule? I am also running on Linux, and would be interested in seeing what you did there, as Jellyfin isn't the only thing I intend to host from the same device.

Thanks again.