In Minecraft 1.15.2 I place a repeating command block with the command

 ??execute at @e[type=minecraft:potion,nbt={Item:{id:"minecraft:splash_potion",Count:1b,tag:

}}] run summon minecraft:fireball ~ ~ ~ {ExplosionPower:1} ??

Then I proceed to throw a splash potion of harming 1 which should summon a fireball at its position. However, the command block does not detect the thrown splash potion