I noticed that Protection resists more firework blast damage during flight and when launching regularly (while I'm in a hole for it to explode on me) than Blast Protection. While in flight with all Protection 4 Netherite armor (except for chestplate as I'm wearing an elytra), a firework with 5 firework stars deal 1 and a half hearts, while when swapping the Protection with Blast Protection 4, the firework explosion deals 3 and a half hearts. As for exploding on my player, a full set of Netherite Protection 4 resists all damage from a 5 star firework, while full Blast Protection 4 takes 1 heart of damage. It may seem like Blast Protection IS resisting some damage, but if you wear full Projectile Protection 4, the firework also deals 1 heart of damage, meaning that the Blast Protection does nothing at all. I also tested Projectile Protection while in flight, it also receives the same damage as with the Blast Protection, again, meaning the Blast Protection doesn't resist firework damage at all. Without armor, the explosion usually deals 7 hearts of damage. The Blast Protection appears to be absent from firework explosions and somehow regular Protection resists it instead.