2.6.2snap1 the import in Lighttable does not display all available drives (Linux).
After the following install the file explorer works correctly
$ wget -nv https://download.opensuse.org/repositories/graphics:darktable/xUbuntu_18.04/Release.key -O Release.key
sudo apt-key add - < Release.key
sudo apt-get update
sudo apt-get install darktable
external drives can only be accessed by snap packages via the removable-media interface, did you connect it ?
that interface also expects that these drives are mounted in common/standard places (under /media or /mnt)
as long as your drives are mounted underneath either of these dirs and the interface is connected the darktable snap should work as expected.
snap connections darktable list
removable-media as connected (or do you see it connected in the software center GUI when you scroll down to “permissions” on the darktable page)
I’m going from memory here but I do remember setting removable media
permission. Removable media then displayed but still no second internal