If you're looking for a different experience, developers on platforms like Game Jolt and Tynker have created standalone "Underwater" clones and story-based expansions. Top Underwater Levels to Play Right Now

Add bubbles and "underwater junk" (like fish or bones) to the background to increase immersion.

A classic in the Water Gauntlet that uses specialized "bubble" decorations and dolphin animations. How to Create Your Own Underwater Level

A Medium Demon level featuring a sunken city, coral reefs, and vibrant underwater lighting.

With the 2.2 update, creators have more tools than ever to simulate being underwater:

Many creators use Force Blocks to simulate water buoyancy, making the cube feel like it’s floating rather than falling. System Requirements for Smooth Gameplay