Custom Piglin summoned to hold weapon/item in each hand will hide the offhand item but will also drop the offhand item when killed or zombified even if ; hand drops are disabled ; gamerule doEntityDrops = false. If Ai is disabled when summoned, both hand items are visible until Ai is turned on.
Can test with :

/summon minecraft:piglin ~ ~ ~-1 {IsImmuneToZombification:1,HandItems:[{id:iron_sword,Count:1},{id:wooden_sword,Count:1}],HandDropChances:[0.00f,0.00f]}

If offhand item is a gold sword, will switch to that item in main hand but will still drop that original offhand item.

Piglin Brutes not showing this issue.