On the Win11 machine, when selecting data sources, there seems to be three ways to reach the same data, user, computer, and source data. Are these alternatives, or does checking more than one route actually backup the same data several times?
I am referring to My Documents which is also under c:\Users\, etc.
The “Computer” shortcut is meant to look like what you see in Windows Explorer and are essentially stored as a kind of environment variable lookup. If you click one, you can see that it adds a path under “Sources” that looks something like %MUSIC%.
If you find the same path by going through C:\Users and click it, you will see that it shows up as a regular path in "Sources.
When the backup runs, the shortcut version gets translated to the current absolute path, before being backed up. At this point Duplicati no longer knows about the special mapping and will treat all the paths the same. Before starting the backup, Duplicati will remove duplicate sources, so it does not work on the same files twice.
For most uses, you can treat the two as the same. But if you are a sysadmin (or like to play around with your system settings) you can change where your My Documents or My Music folder is located. If you do that, the shortcuts will reflect this change on the next backup, the direct paths will naturally not change.
Very few people change these folders this in practice, so it is mostly relevant if you move machines or import a backup on another machine.
Not sure where you see “User, Computer, and Source Data”, it should only be “Computer” and then the actual drives.