Divide sugar, maple syrup, butter, and cinnamon between both halves of acorn squash.
Add 1 cup of water into an electric pressure cooker (such as Instant Pot®) and place trivet inside. Carefully place squash halves on top of trivet. Lock lid and close pressure valve.
Select High pressure according to manufacturer's instructions; set timer for 5 minutes. Allow 10 to 15 minutes for pressure to build.
Release pressure using the natural-release method, about 7 minutes. Release any remaining pressure according to manufacturer's instructions. Unlock lid, carefully remove squash, and serve.