$ sudo apt-get update
$ sudo apt-get install remmina-plugin-nx 

remmina-plugin-nx is installed in your system.

Make ensure the remmina-plugin-nx package were installed using the commands given below,

$ sudo dpkg-query -l | grep remmina-plugin-nx *

You will get with remmina-plugin-nx package name, version, architecture and description in a table

remmina-plugin-nx package basic information: