Historically, every gold-related item in Minecraft (aside from ores and raw gold) has had a chance to generate inside a ruined portal chest. This is not the case for golden nautilus armor.
To reproduce (in-game)
/give @s chest[minecraft:container_loot={loot_table:"minecraft:chests/ruined_portal"}]Place and open as many chests as you like until you are convinced there is no golden nautilus armor in ruined portal chests
Closing as a Duplicate to track the issue in one ticket.