To breathe underwater in Horizon Forbidden West, you need diving mask, is a Special Gear item that you can only craft during The Sea of Sands main quest, which is a quest where you seek out the POSEIDON side function. Seas of Sands unlocks at the end The Eye of the Earth The main task.
In The Sea of Sands, you’ll travel to the ruins of Las Vegas and meet a group of divers trying to retrieve belongings from Dunehollow, the flooded rooms below the Tower of Tears. This is also where Aloy believes POSEIDON will be, so your goals align well with those of others. They attempted to dive using a device called a diving bubble, and nearly drowned in the process. Once you’ve obtained their compressed air capsule and hunted down a Frost Bellowback for its synthetic membrane, you can then craft a diving mask, much better than a diving bubble.
Once you’ve built your diving mask, breathing underwater is a simple matter of diving into deep water. You don’t have to manually equip it – Aloy wears it automatically when underwater – and there’s no limit to how long you can stay underwater when using it.
https://www.gamepur.com/guides/how-to-breathe-underwater-in-horizon-forbidden-west How to breathe underwater in Horizon Forbidden West