Select the SAUTE function on the Instant Pot, heat the oil, and season the chicken thighs with salt and pepper. Place the chicken skin-side down and sear until well browned.
Pour in the water to deglaze the pot, scraping up any browned bits with a wooden spoon. Turn off the SAUTE function.
Stir in the garlic, honey, Dijon mustard, and whole grain mustard. Add the halved potatoes and sliced carrots to the pot.
Adjust seasoning with additional salt and pepper if needed, then secure the lid and set the valve to the sealing position.
Choose the MANUAL or PRESSURE COOK setting on high pressure and cook for 8 minutes.
Once the cooking cycle ends, perform a quick release of the pressure. Open the lid carefully and check for doneness.
For a thicker sauce, use the SAUTE setting to reduce the liquid slightly. Garnish the dish with freshly chopped parsley before serving.