There is an issue with the Moodle app 4.x which prevents users from navigating nested folders inside courses - described in https://tracker.moodle.org/browse/MOBILE-4084

We used the workaround mentioned there, by enabling "Display description".

We notice excessive network and storage use. Just navigating into a folder which has 28 MB of pptx files, even without enabling the "make available offline" option, network and storage use goes beyond 28 MB.

We have not tested this with the 3.x version of the app without enabling  "Display description".