This is a very simple mod that makes the backpack invisible to other players.
Simply place the backpack in a bag, place the bag in a backpack, and then open the backpack and look at the backpack while looking at your feet.
You will see a “packet” floating in the air and can only move the backpack to where you place it.
It also lets you walk while it is floating.
This mod requires a SkyUI compatible patch to function.
If you do not have SkyUI installed, it will not work.