I use NordVPN and Transmission from Dietpi and it's not useful to use this in combination, because NordVPN does not allow Port forwarding.
https://nordvpn.com/blog/port-forwarding/Does port forwarding work with a VPN? Port forwarding and triggering could work with a VPN protocol in general, but not with NordVPN. Our apps block almost all port communication from within your device except for the ones most commonly used by popular applications. This was a tough decision that may inconvenience some users, but we’d like to explain why we did this. Browsing the internet with open ports opens you up to a number of security risks. Blocking access to all ports except those that are essential for our VPN to operate and for you to enjoy the internet is part of how NordVPN keeps you secure. We wouldn’t be able to maintain our excellent security track record otherwise. wrote:
port forwarding is essentialliy for seeding. It's possible to leech, but not to seed. So for many funny things, you cannot combine this.
I have not found a solution to configure transmission for SOCKS5, which NordVPN supports;
Also on my installation with dietpi i've added Plexmediaserver. This is a really funny thing, but if you use NordVPN you cannot access your plexserver externally anymore. Here we have the same problem: NordVPN does not allow Port Forwarding, so your Plexserver will not bee accessable anymore. Plex uses as standard Port 32400.
So I cannot follow the recommentation of DietPi to use the combination with NordVPN.