Here is the full list of all 25 Manifold Garden achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Shrink Down Into a Small Model of a Level
See the Ending
Grow a Double Gravity Tree
Open the Final Door
Complete the Orange Level
Complete the Rainbow Level
Complete the Purple Level
Complete the Yellow Level
Solve a Puzzle Involving Portals
Change the Color of a Cube
Redirect Water Through a Portal
Complete the Green Level
Power on a Water Wheel
Redirect Water Using a Cube
Grow a Tree
Complete the Red Level
Grow a World
Complete the Blue Level
Collapse the Dark World
Enter the Dark World
Activate a Laser Beam
Fall from a Great Height
Earn Every Achievement
Use a Hidden Path to Return to an Earlier Level
Complete the Game Without Placing a Single God Cube