Wash and peel the sweet potatoes. Cut them into roughly 1- to 1½-inch chunks so they cook evenly in the Instant Pot.
Pour 1 cup of water into the Instant Pot insert and place the metal trivet inside. Add the chopped sweet potatoes on top of the trivet in a single layer if possible.
Secure the lid and set the valve to sealing. Cook on high pressure for 8 minutes. If your pieces are larger, increase to 10 minutes.
When cooking finishes, allow a 5-minute natural release, then carefully quick-release any remaining pressure and open the lid.
Drain any excess water from the pot, return the sweet potatoes to the insert, and add butter, milk, maple syrup, ground cinnamon, salt, and pepper.
Mash with a potato masher or beat with a hand mixer for a few pulses until smooth and creamy. Stir in lemon juice if using to brighten the flavors.
Taste and adjust seasoning, adding more salt, cinnamon, or maple syrup as needed. Serve warm garnished with a pat of butter or a sprinkle of cinnamon.