How to tame a nautilus and get nautilus armor in Minecraft
Copper, iron, golden and diamond nautilus armor cannot be crafted.

Diamond Nautilus Armor: 11 armor points, toughness 2, and the starting point for netherite. Nautilus armor protects a tamed Nautilus, the mount you ride underwater. All nautilus armor works the same; the Iron Nautilus Armor page explains it.
It cannot be crafted; it can be found in chests.
This item has no crafting recipe.
Copper, iron, golden and diamond nautilus armor cannot be crafted.
The upgrade works on every diamond tool, weapon and armor piece, including the Diamond Hoe, the Diamond Spear, Diamond Horse Armor and Diamond Nautilus Armor.
It can be found as loot in Buried Treasure, Shipwreck and Ocean Ruins.
It protects a ridden nautilus in underwater fights. It is an ingredient in one recipe: Netherite Nautilus Armor. Worn by: Nautilus and Zombie Nautilus.
No: only one per inventory slot.