On a 6-quart Instant Pot, select Normal/Medium Sauté. Add 2 tablespoons of the butter and melt.
Add the shallots and mushrooms, then cook, stirring occasionally, until the mushrooms have released all of their moisture, about 5 minutes.
Add the rice and cook, stirring, until translucent at the edges, 1 to 2 minutes. Stir in the sage, broth and 1½ cups water, then distribute the mixture in an even layer.
Press Cancel, lock the lid in place and move the pressure valve to Sealing. Select Pressure Cook or Manual; adjust the pressure level to Low. Set the cooking time for 3 minutes.
When pressure cooking is complete, quick-release the steam by moving the pressure valve to Venting. Press Cancel, then carefully open the pot.
Vigorously stir in the Parmesan and the remaining 4 tablespoons butter, adding the butter one piece at a time.
Taste and season with salt and pepper, then stir in 3 tablespoons of the chives and the vinegar. Serve sprinkled with the remaining 1 tablespoon chives and with additional Parmesan on the side.
