The appdata folder is designed for files that are not visible to the user. Things like configuration files that it doesn't make sense for them to be able to see, edit or work with individually. They can just see the amount of storage being used.
If you want the user to be selecting specific files, it probably doesn't belong in the appdata folder. You could create a regular folder for your app, and set that as the starting point for the picker by calling "setParent" on the view with the id of the folder.