How to Reproduce:

Execute the following command at your location.

execute summon minecraft:item run data merge entity @s {Item:{id:"minecraft:stick",Count:1b}}

Rather than receiving a stick, you get nothing. This is likely because the game notices that the item is air by default and deletes it before the run subcommand can do anything.

What to Expect:

I would expect 'execute summon minecraft:item' to summon an item that wouldn't get deleted until at least the end of the tick, so I can do what I will with it.