If I summon an invulnerable item that you can't pick up with the command /summon item ~ ~ ~ {PickupDelay:32767,Item:

,Invulnerable:1b} and set the item on fire for about 5 seconds the item will be gone. But if I use the command /say @e[distance=..5] it says the item that I have just burned. So that item does not burn up, it becomes invisible.