With this datapack every item that player dropped(from his inventory, or after his death) will glow.

If you want this datapack, but you are too lazy to install it, you can just put the repeating command block{seted to always active} on world spawn and put this command into it: execute as @e[type= minecraft:item, nbt= {PickupDelay:40s, Age:0s}] run data merge entity @s {Glowing: 1b}