The bug

Unable to set "LeftHanded" to "1b" for piglins.
Still use right hand to hold items or weapons.

How to reproduce

1. Summon a piglin with a weapon and left handed:

   /summon piglin ~ ~ ~ {LeftHanded:1b,HandItems:[{id:iron_sword,Count:1}]}
   

   → Notice that the piglin is still holding the weapon with it right hand.

2. Use the following command:

   /data get entity @e[type=minecraft:piglin,distance=..3,limit=1]
   

   → Notice that LeftHanded is still 0b