VPN

There is no port forwarding at Nord. Designated servers offer no technically advantageous feature set for P2P. They simply keep the P2P traffic separate from other traffic so that non P2P server latencies remain lower and more responsive. They also typically host P2P servers in jurisdictions where they are less likely to be hassled for it.

UPnP is not compatible with using a VPN. Do not activate UPnP on your router or client if you are using a VPN to route the traffic. This can be used as a parallel attack vector and can leak data outside of your designated VPN route.