The third one, as the name tells us, is more difficult. Which is nice, since Subnautica has a lot of stuff to explore. In other words, it's a game mode for people who want to explore without having to bother with surviving. It also leaves all the items in your inventory after you die.
The second game mode basically removes every mechanic that is related to surviving, such as the aforementioned hunger and thirst mechanics. The first one pits the player against the elements and forces them to think about food and water through its thirst and hunger mechanics.
Has a mode for people who just want to explore Subnautica has four game modes: survival, freedom, hardcore, and creative.
