[Android] Cannot Access Downloaded File

[dinobagio]

Describe the bug
I browse my private folder, and click on "..."
Then I choose download,
It downloads then download manager tells me download finished, and open a popup to choose an app to open the latter.
But what ever app I use, it tells me 'access denied' and indeed I can't ever retrieve the downloaded file, I guess it's downloaded within the app data, unavailable to the outside world.

Expected behavior
I'd like either being able to open/edit file with a chosen app, and then being able to retrieve file in my file browser locally.