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(R)) 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.
