If you have a heavily modded save file from 2021, disable auto-updates on Steam and play in offline mode until your mods update.
Released in late 2022 and refined through early 2023, the Living Large update brought Subnautica onto a unified version of the Unity engine, backporting several key features from its sequel, Subnautica: Below Zero . The v29.03.2023 period followed shortly after the (March 7, 2023), which ensured the game was "Verified" for handheld play. Key Features and Changes Subnautica v29.03.2023