Put all dry ingredients into the Instant Pot inner pot, add 2 cups water, and stir. Secure the lid, ensuring the valve is turned to the Sealing position. Press the Pressure Cook button and set the time to 1 minute.
When cooking is compete, turn the valve to the Venting position to release the pressure. Remove the lid.
Add the rum to the pot and give it a stir or whisk. Ladle the buttered rum into 4 mugs and garnish each with a cinnamon stick.