The bug
When a left-handed enderman attacks a player, they will swing their left arm differently compared to right-handed endermen.
To reproduce
Summon an enderman
/summon minecraft:enderman ~ ~ ~ {Attributes:[{Base:-10.0d,Name:"generic.movement_speed"},{Base:0.0d,Name:"generic.attack_damage"}],LeftHanded:1b}
Either attack it or look at it in the eyes
→ ❌ It's swings it's left arm in a weird way
Duplicate MC-124195.