NordVPN has already released a debian package which i’ve tested and works on OSMC. This package allows connections using the NordLynx protocol as well as OpenVPN, and is officially supported.
Instructions to get this installed are at: Installing NordVPN on Debian, Ubuntu, Raspberry Pi, Elementary OS & Linux Mint | NordVPN Support
In addition, I had to disable IPv6 by adding the below lines to /etc/sysctl.conf
# Disable IPv6 as suggested by https://support.nordvpn.com/Connectivity/Linux/1047409212/How-to-disable-IPv6-on-Linux.htm
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
net.ipv6.conf.tun0.disable_ipv6 = 1
I’ve been able to connect trivially with that.
osmc@osmc:~$ nordvpn status
Status: Connected
Current server: us8531.nordvpn.com
Country: United States
City: San Francisco
Server IP: 192.145.118.142
Current technology: NORDLYNX
Current protocol: UDP
Transfer: 115.92 MiB received, 1.77 MiB sent
Uptime: 6 minutes 19 seconds
Hope this helps.