Originally Posted by Nefertari
I can't split it and have 10 and 10

You should be able to. In the keyboard UI, hold Shift when drag and dropping a stack in your inventory (or right click, split item); you can drag the diamond icon in the split-stack-window slider to adjust how many to split, or use the left/right arrow keys. In the controller UI, select a stack, open the actions menu and select split.