Rashi: Those incarcerated in Galus. Radak - they have no power to leave the authority of the Goyim. Also "Asher ba'Choshech" applies to those in Galus.

Malbim: Yehudah and Binyamin were scattered and exiled under Nochrim who fettered them in iron chains - "Lehotzi mi'Masger Asir" (42:7).

Radak: Also this applies to those in Galus.

Malbim: The 10 tribes were exiled to Chalach and Chavor; they are not subjugated under Nochrim. However, they are in closed places; no one knows their place, and it is as if they are in darkness.

Radak: He provided for them all their needs when they left Galus.

Malbim: The 10 tribes were not incarcerated. Their return to their rest is compared to a flock that Hashem tends - "k'Ro'eh Edro Yir'eh" (40:11). Sometimes a shepherd must conduct the flock to the Midbar, to distance them from plunderers, or to find pasture. This will not be needed; no travelers will harm them, and they will find all their needs.

Rashi citing Targum Yonasan: They are rivers.

Radak: They are high places ¹ . The same applies to "va'Yelech Shefi" (Bamidbar 23:3). Normally, one does not find pasture for animals in mountains, for there is not water there. So the places where travelers do not normally find their needs, they will find their needs.