'SSH connections' are possible via NoMachine provided that on the server-side a NoMachine server product which supports SSH is installed. In order to connect by SSH protocol to a remote Mac server it's necessary to enable the Remote Login and start the SSH server on the Mac.

To do that, follow these steps on the Mac computer where you have installed any of the NoMachine server products from the Enterprise range:

Open System Preferences->Sharing.

Check 'Remote Login' and select appropriate user(s) who will be able to login remotely by SSH.

Fig. 1 - On your macOS: System Preferences->Sharing-> Check 'Remote Login' and choose which user to enable

Ref. https://support.apple.com/guide/mac-help/allow-a-remote-computer-to-access-your-mac-mchlp1066/mac