NordVPN support states the following:
Unfortunately, you will not be able to set up a NordVPN connection on RouterOS version 7.5 or newer, as there is a problem with certificate importing - which is required to establish a VPN connection to our servers.
The MikroTik support team confirmed that their team is working on resolving the problem. In the meantime, you may try downgrading your RouterOS version to 7.4.1, importing the certificate (step 2 in our guide), and then upgrading the RouterOS version again.
Alternatively, you may use the working 7.4.1 RouterOS version until the problems from MikroTik’s side are resolved.
We apologize for the temporary inconvenience this may cause.