My shield doesn't work

When I was experimenting in the test chambers structure, I was ready with the Netherite armor complete with enchanted golden apple night vision potions and with the wind charge and the mace ready to defend myself, but when I am ready I use the shield first to do The zombies retreat, but I don't know what happened, I move the shield and it does nothing to protect me from the hostile mobs.

Thank you very much. I love your game