I have a problem with the alt button not showing all interactable objects. Feels like a half assed implementation.
Divinity did the same thing. You needed a mod, which I happily grabbed, if you wanted things like barrels and crates to show up for the alt. Might need to wait for a mod for that one here too. I think it has to do with the fact that if you hold alt and click containers that are lootable you loot the entire container.
I would much rather have to right click and add to inventory the very select few containers or backpacks I want in my bags, then have majority of the containers hidden from alt view.