When you access the physical desktop remotely, you are connecting to its physical display. This functionality is provided by both the free to download NoMachine for Win/Mac/Linux and Raspberry packages, and the NoMachine Enterprise Desktop product.
On Linux, when connecting to the physical desktop which doesn't have an X server running (e.g. it's a headless machine), NoMachine is able to use its own display service (that is an embedded X server) to let users connect seamlessly to a physical desktop running in the background on the remote machine. Pre-requisite is having a desktop environment installed. This ability is enabled by default in NoMachine free version, but can be activated also for the other server types. See: https://www.nomachine.com/FR10L02842 for more details.
If multiple users are supported and they connect, they will all see the same desktop. However, if you run Linux, by installing any of the products from the NoMachine for Enterprise Terminal Server range, instead, you can run "virtual desktop sessions". The virtual desktop functionality allows individual multiple Linux desktops to run on the same host. Each user can have their own personal 'virtual' Linux desktop according to how the Administrator has configured it.
The virtual desktop functionality is not available on Windows or Mac.
You can run a 'virtual desktop' session, provided you have one of the following installed on a remote Linux host: Workstation, Small Business Server, Terminal Server, or Enterprise Terminal Server. Use either NoMachine or Enterprise Client to connect. As long as the virtual desktop functionality is enabled, the connection GUI will allow you to run a virtual desktop, or alternatively a 'Custom session' (virtual single applications on Linux). Connections by the web are also supported.
Depending on the type of server product installed, you will be able to run from 4 virtual desktops to an unlimited number. User numbers are unlimited in that you can have as many user name accounts as needed. It is the number of concurrent virtual desktops which is considered. For example, in the case of Workstation, only 4 virtual desktops will be allowed at any given time; with Small Business Server that number is 10, and with the Terminal/Enterprise Terminal Servers that number is unlimited.
Differences between NoMachine and NoMachine Workstation