Full Disk Backup (with quite a few limitations noted there though)
How to set up a full Windows OS Backup with Duplicati 2.3
has some more notes, including its current lack of documentation.
Possibly this isn’t your request though. Are you looking for an image backup
or a traditional Duplicati file backup with alternative way to pick mount point?
If you’re into heavy customization of folder selection, image might not fit that.
I’m also not sure if one can do file-oriented restore, but for now I’d guess not.
For your part, maybe you can further detail what you’re trying to accomplish?