Currently, there is for Stranded Deep. Unlike games with highly flexible engines like Minecraft or Valheim , Stranded Deep’s multiplayer architecture is deeply tied to a peer-to-peer (P2P) system designed specifically for two people. Technical Hurdles
Stranded Deep ’s isolated, sun-drenched islands and shark-infested waters provide a visceral survival experience. While the game was originally a solo journey, developers eventually added to allow players to face the Pacific with a friend. However, many players find themselves with a group of three or four, leading to the persistent question: is there a 3-player mod for Stranded Deep? The Current State of Multiplayer
Supports 2-player online co-op and local split-screen.
A utility tool that adds a HUD for health and hunger, fast travel, and map controls.
Stranded Deep 3-Player Mod: Is It Possible to Expand Your Tribe?
While you can’t add a third person, you can use mods to significantly overhaul the 2-player survival experience.
Community discussions on Steam and the official forums highlight several reasons why a 3-player mod hasn't been realized:
Many of the game’s core systems—including the starting life raft and resource spawning—are hardcoded for a maximum of two occupants.