@cernel Well what a VPN does is to redirect all of your internet traffic through the servers of the VPN provider. To express it with the NordVPN Documentation (not sponsored btw):
Port forwarding and triggering could work with a VPN protocol in general, but not with NordVPN.
So while there's nothing speaking against Port Forwarding with a VPN in general, your VPN provider would need to explicitly support it, i.e. forward all traffic they get on a certain port back to you.
But I'll update the description regardless, because you're right. This might be a common pitfall nowadays.