As the message suggests, USB devices are not supported with the version you are using. You should consider updating your remote server software to the latest version (5). File transfer can be executed either by sharing a device (folder, usb etc) or directly via the Monitor (!M icon). See here for more details:
https://www.nomachine.com/sharing-files-between-computers
If you need some tips setting up file-sharing for the legacy 3.5.0 software, I suggest you contact the team via the website (Contact us -> General Enquiries). The forums are dedicated entirely to the latest NoMachine software (version 5 or version 4).