Hi, when you try connecting from the Macbook to the Linux server, do you see a black screen or a message? If it’s a message, can you show us a screenshot? Not seeing the local LAN connection of the Linux server on your macbook might be because maybe the macOS is not configured for LAN access in Privacy & Security in the system settings? I know you said it was working before, maybe something changed when you updated NoMachine to version 9.2.18? What version of macOS is it?
(P.s ideally you should update your legacy v7 Linux server to a more recent version. If you prefer to update first to v8, please contact us for a private link to the packages as they are no longer public.)