on the current version of Minecraft on Windows 10 Neither the 'Iron Belly' or 'Sail The 7 Seas' achievements can be unlocked. Ive spent four days troubleshooting and found no way to unlock them which means its a problem with the current build. Perhaps the changing of the terrain from 1.18 has messed with the biomes registering as the ones needed to unlock 'Sail The 7 Seas'. As for 'Iron Belly' im at a loss. They just dont work and need fixing