Setting a damage value on to a slot
Solution 1:
This command prevents items from stacking. If you put it into a repeating command block, then items should no longer stack, as soon as they were dropped at least once (it will not break stacks that already exist as stacks)
/execute as @e[type=item] run data modify entity @s Item.tag.PreventStacking set from entity @s UUIDMost
Note: I use Minecraft 1.14.2 and this command may not work in older versions