The 1.21.30.21 Preview changelog states:

• Any item or block which can be crafted must inherit the highest rarity of its crafting ingredients

Steps to reproduce:

1. Take a piece of gunpowder, any dye and any mob head
2. Craft a firework star with them
3. Using the obtained firework star, craft some firework rockets

Observed result:
The crafted firework star and firework rockets have a rarity of Common.

Expected result:
If crafted with a head/skull other than the Dragon Head and the Wither Skeleton Skull, The crafted firework star and firework rockets have a rarity of Uncommon.
If crafted with a Wither Skeleton Skull, the crafted firework star and firework rockets have a rarity of Rare.
If crafted with a Dragon Head, the crafted firework star and firework rockets have a rarity of Epic.