Hey David,
The courses are usually released using the latest version of Blender, unless a new version of Blender is released during production.
Geometry nodes have changed with every version of Blender since Geometry nodes in Blender was first introduced.
The Duplicate Elements node is available from v3.2+
I personally never used v3.1 much because I found it quite buggy, and if I remember 3.2 was released fairly soon after anyway.
Its normally recommended to use the latest version when starting a new project, but once started stick with that version.
Hope this helps.
