It took me ages to enable the files permission for emacs.

The easiest way is:

1. Go into your phone’s settings and search for ‘all files access’
2. In the Apps results subsection, there should be an option for ‘All files access’, tap it
3. Then tap on ‘All files access’ in the Special access list
4. There should be a list of apps with ‘All files access’ permissions
5. Search for ‘emacs’
6. Enable the permission for it

That should be it.