I'm not sure if this is going to be useful, but here are the items I have received while bartering: Magma Cream, Glowstone, Raw Porkchop, both types of mushroom, both types of fungi, shroomlight, leather, nether quarz, nether brick, rotten flesh, obsidian (1 piece, very rare), gravel, soul sand, enderpearl, fire charge.
If you prevent the piglin from moving, you can throw whole stacks of ingots at them and they will slowly barter them all. They will pick up anything made from gold, but only gold ingots seem to result in trades. CrCl3 (talk) 16:28, 14 February 2020 (UTC)