A free mod for Witcher 3, by Groznui.
This is a simple mod that adds two new options to the game. One allows you to sort your inventory by level, and the other by the damage or armor rating of your items.
You can set it to whatever you prefer, and it will stay that way even after you close your inventory, or open it again. It also ensures that multiple stacks of the same item are sorted together.
It should be pointed out that this is not a big change, as it only changes the way your inventory is sorted. It does not affect how you acquire your items, or how you level up, or how you get your weapons and armor.
The reason why this mod was released this is that there is a bug in the way the game is sorted. It has to do with the way items are sorted in the list.