Depending on your subscription plan, you can run RealVNC Server in different modes to provide remote access to computers in different circumstances, and meet different needs.
This is either the desktop of the currently logged in user, or else the login screen.
Subscriptions with offline licensing only
RealVNC Server automatically stops (and RealVNC Viewer users are disconnected, and cannot reconnect) as soon as the current user logs out. The login screen cannot be remoted.
Subscriptions with Virtual Mode feature
Linux platforms only
Instead, they gain access to a persistent private workspace. The virtual desktop is not destroyed until RealVNC Server is explicitly stopped. The login screen cannot be remoted.
You can start RealVNC Server in Virtual mode on an ad-hoc basis or run it as a service to create virtual desktops on demand.
RealVNC Server can run in Service Mode and User Mode concurrently, though this is not generally useful, and likely to result in port conflicts.
RealVNC Server is designed to run in Virtual Mode as many times as you have computers in your subscription's capacity (referred to as desktops). It can safely be run concurrently with either other mode.