I have configured my openvpn client on openwrt to connect to nordvpn using this :
vpn in well mounted :
I have two lan ports in my router.
First Lan port is connected to my box
I want to use the second lan port to connect a device (tv or something else) and I want that the device use the vpn tuning
A regular installation will route all Internet usage from any router network through the VPN. If that doesn't work, you need to troubleshoot that first.
Policy routing is only necessary if you want some things to continue to go to the Internet directly instead of via VPN while others do use the VPN.
Yes that's why VPN is not working-- the simplest way to set up VPN is an extension of lan->wan routing. So plug the WAN into your home network and the PC on lan.