I’m trying to install Syncthing on a Samsung Galaxy Tab A. I am able to select the Download folder and a base-level folder. However, if I create a sub-folder inside of the download folder and attempt to select it, I get the error:
“Sorry. The selected folder cannot be used. Please select a folder on the internal or external storage.”
I think it helps to show the internal storage root, click that on the left bar of the file picker dialog and then go deeper from there. Using the shortcut by clicking Downloads on the nav bar, Android generates URIs which the app cannot translate for Syncthing’s native file access.