Had been struggling to get the NordVPN linux app to work on SteamOS. Had it working at one point by blindly copy pasting a load of stuff in Konsole, turning off the protections on Steam etc. Only to have it wiped on an update. Finally found a half-way house that seems to work OK (although it means the Deck is limited to non-Nordlynx servers).
Here’s the guthub link, download the pack, save somewhere then copy the Nordvpn.client from the Binaries folder and save it to your desktop. Follow the guide to save your username and password using Terminal, then you should be golden. The app finds the best/recommender server and connects you. Beats having to download the profile from the website and manually add it to OpenVPN.
Found a bug unfortunately. On reboot of the Deck, the secret keys are wiped, so you have to go into terminal each boot and re-enter. If anyone can work out that part, then we’re good.