According to the NordVPN, you should use the following steps to install NordVPN on Linux:
Download the NordVPN client by opening a command line prompt and typing:
sh <(curl -sSf https://downloads.nordcdn.com/apps/linux/install.sh)
Log in to your NordVPN account by choosing:
NordVPN login
Connect to a NordVPN server by choosing:
NordVPN connect