Shields should be able to be made out of not just iron but gold diamond and netherite. With each allowing a certain amount of damage to bypass the shield and hit you but also dealing the remaining damage to the shield. The enchantments that should be allowed on shields are projectile, fire, blast, and normal protection. Each one just reduces the damage the shield takes from each thing. Except fire protection would stop fire from bypassing the shield and going onto you, and the new enchantment is axe protection, it would stop the axe from doing some damage to the shield. Maybe the enchantments can only go up to level 3 (III) for shields. But fire protection would just be 1 (I).