You can show the folders on a document report by text mode.
displayname=Folder
listdelimeter=<br>
listmethod=nested(folders).lists
textmode=true
type=iterate
valueexpression={name}
valueformat=HTML
Optionally, you can also show the parent folders name in the column.
displayname=Folder
listdelimeter=<br>
listmethod=nested(folders).lists
textmode=true
type=iterate
valueexpression=CONCAT({parent}.{name}," / ",{name})
valueformat=HTML