Netherite Nugget is a mining drop from ancient debris. 9 netherite nuggets can be crafted into 1 ancient debris. Unlike the other nugget-based ore rebalances in the mod, Ancient Debris can only be obtained in block form using silk touch on a Netherite pickaxe, but without silk touch, there is a chance for more than 9 nuggets.
Diamond Pickaxe = 1-6 netherite nuggets
Netherite Pickaxe (without silk touch) = 4-12 netherite nuggets