If you use the /damage command on a player while they're using a shield, the "block attack" sound will play, but the shield will not get damaged or play the "got attacked" animation.
How to reproduce:
Set up a command block that hurts the player with mob_attack by an entity that is in front of them (e.g. "damage @p 1 mob_attack by @e[type=!player,sort=nearest,limit=1]"{}){}
Give the player a shield
Hold right-click while holding the shield
What is expected to happen:
Hurt the shield's durability and lower the model in first person, like a normal attack
What happens instead:
The shield sound plays, but it doesn't get damaged
SilicatYT
Works as expected. The minimum incoming damage to cause durability loss on a shield is 3, so the command in the description is incorrect. Using a value of 3 or more correctly applies durability loss.