The Plex server is in a double-NAT situation. Both the ISP router and your Netgear router are performing network address translation.
One solution is to eliminate one of the NAT processes. You could ask your ISP to place their router in “modem mode.” It will provide one public address to the Netgear router, which then provided 192.168.x.x address to all devices. Alternately, you can run the Netgear in Access Point mode, disabling its NAT processes. Everything on your network will then have a 10.x.x.x address (which you said you do not want to do).
A second solution is a double port forward.
- A port forward statement in the ISP router points to the 10.x.x.x address of the Netgear router.
- A port forward statement in the Netgear router points to the IP address of your Plex server (192.168.x.x).
The Netgear router will need a fixed 10.x.x.x address, either statically configured on the Netgear itself or assigned by the ISP router.
The Plex server will need a fixed 192.168.x.x address, either statically configured on the server or assigned by the Netgear router.
