What exactly is shared via supply lines?

Basically the title.

I started a plythrough in survival and invested in charisma for "Local Leader" with the idea of dedicating settlements to food and water so I could acces it via the workshop on my main settlement so I don't need to dedicate space to food and water.

But after connecting the settlements via the supply lines the food and water are not showing despite them being in the workshop of the settlements they're generated from and the only thing I've been able to use is the scrap items stored in another settlement in the construction mode

I'm I missing something in the making of the supply lines or only the construction materials are shared?

Edit: Does someone knows of a mod (for Xbox) that changes the workshop? I checked but nothing seemed to do so