Experienced players note that the game is already prone to bugs, desync, and server instability with just two people. Doubling or even slightly increasing the player count would likely break critical game systems.
With three players, the early-game grind transforms into a strategic operation. One player can focus on gathering fibrous leaves for lashings and a water still, another on crafting crude tools and a fishing spear, while the third builds a shelter and a campfire. What might take a solo player an entire in-game day can be accomplished in a few hours.
There is currently for Stranded Deep that increases the player count to 3 . The game is hard-coded for a maximum of two players in both local and online co-op modes.
While there is no widely available, stable "plug-and-play" mod that simply increases the player count to three, the modding community has focused on expanding the world itself to accommodate the feeling of a larger scale. How to get the Stranded Wide MOD for Stranded Deep