How can I make a piece of armor give the player no protection?

Solution 1:

Armor has an NBT value called operation, accessed like this:

{AttributeModifiers:[{Operation:0}]}

Operation is a value for how much armor protects the player. Operation:0 means the armor is purely cosmetic.

Try this:

/give @s minecraft:iron_boots{AttributeModifiers:[{Operation:0}]}