When I get the error that NordVPN cannot update because I need to quit the application run these commands
Run this to easily find the process id:
sudo snap refresh nordvpn
You will get a response like:
error: cannot refresh “nordvpn”: snap “nordvpn” has running apps (nordvpn), pids: 10116
Enter the process id into this command to stop NordVPN
kill -9 10116
Then NordVPN should be able to refresh properly
sudo snap refresh nordvpn
nordvpn 3.20.3 from NordVPN✓ refreshed