To turn off the NoMachine automatic upgrade from v.6 to v.7, remove all the UpgradeServer lines from the configuration file for updates, update.cfg  and save changes.

In this way, the NoMachine programs v.6 will still check our repositories every two days, but only to see if a new version 6 is available. They will not fetch instead the repositories for v. 7.

The configuration file for updates, update.cfg, is:

Linux:
/usr/NX/etc/update.cfg

Windows:
C:\Program Files (x86)\NoMachine\etc\update.cfg
C:\Program Files (x86)\NoMachine Enterprise Client\etc\update.cfg

macOS:
/Applications/NoMachine.app/Contents/Frameworks/etc/update.cfg
 

UpgradeServer lines will look like the following, remove the whole line starting with UpgradeServer and ending with -----END CERTIFICATE-----: