Cannot drag&drop images from another drives

I'm sure this is due to flatpak nature of seeing things. However there's a setting that enables flatpak environment to take into consideration all drives mounted on /mnt /run and other dirs that are not /media.

Flatpak GIMP had similar problems with not seeing the phone images, as documented here:
https://gitlab.gnome.org/GNOME/gimp/issues/4372#note_670435

However, devs found the solution:
_Ok I think I found the right permission for this. This /run/user/ is basically the $XDG_RUNTIME_DIR env variable and there is a special permission variable in flatpak for this. GIMP's flatpak is rebuilding with this additional permission._

Please fix this for Viber.

Start by locating the Flatpak manifest or permission configuration for com.viber.Viber and compare its filesystem access with the permission described in the linked GIMP issue. Test dragging images from drives mounted under /mnt or /run, including phone images, and confirm that the packaged app can access them without affecting other file access behavior.

Written by the indexing model from the issue text.