Hello,
adding an option to swap Control and Command modifiers on the remote desktop was implemented in 9.0.188. Are you using v9 on both client and server sides?
The new option is added in connection menu -> Input. You can see a screenshot in “Guide to the Functionality in the Menu Panel on Windows”. The label is “Map Ctrl to Cmd and Win to Ctrl”. When this option is not enabled, instead, the user has to use the remote modifier for applying keyboard shortcuts inside the NoMachine session.
https://kb.nomachine.com/DT08U00291#3