This article applies to NoMachine client for Linux.

The pointer highlight feature allows to easily locate the mouse cursor on the screen upon pressing the ctrl key.

When the pointer highlight is enabled on the NoMachine client host, the Control key is not sent to the remote desktop, even if the “Grab the keyboard input” option is enabled in the client settings.

Whichever Ctrl key combination (e.g. ctrl+c) pressed on the user's keyboard will be therefore ineffective in the NoMachine session. 

In this case it's necessary to force the NoMachine client using an alternative method to grab the ctrl key. To do that, launch the client from command line with the --activegrab option:

    --activegrab

   When the setting 'Grab the keyboard input' doesn't catch all keys, use this
   option to force a different grabbing mode. The client will catch keys only
   when the cursor is inside the window.
 

    For example:

    /usr/NX/bin/nxplayer --activegrab

Please refer to the article about How to send 'Option+Click' from Linux to macOS using the activegrab option. https://kb.nomachine.com/AR10Q01058