The file is located here:

%localappdata%\ORS\DragonflyNN\preferences.xml

where NN is the Dragonfly version number, without dots. So for example, the preferences for Dragonfly version 4.1 are stored here:

%localappdata%\ORS\Dragonfly41\preferences.xml

If you need to copy a preference file from one machine to another, you should just copy the file itself instead of using the Save as/Load from feature of the Preferences UI.

There is no preferences.xml file in the All Users folder (C:\ProgramData\ORS\Dragonfly41)