Minecraft wiki entry for Shield, associated text: Melee attacks, except by axe-wielding mobs or by a sprinting player wielding an axe, however even without sprinting an axe still greatly decreases the durability
Normal, tipped and spectral arrows
Arrows are totally deflected and can hit other targets.
Status effects do not carry through to the blocker‌[JE only].
Flaming arrows
Burning does not carry through to the blocker‌[JE only].
Tridents
Snowballs and eggs
Spines from pufferfish
Bullets from shulkers
The levitation effect does not carry through to the blocker‌[JE only].
Spit from llamas
Fireballs, such as from blazes and fire charges
Burning does not carry through to the blocker.
Direct hits from ghast fireballs
These still cause environmental damage.
Explosion damage from creepers
TNT that another player lit
Ravager headbutts
These still knock the blocker back by about 3 blocks.
Blocking these strikes can stun the ravager for a moment, and it roars afterward.
Ravager roars are blocked but still knock back the blocker.
Bee stings are blocked, but bees continuously attack until the player stops blocking and the player is stung.
Beam attacks from guardians or elder guardians (but only in 50%)