Place the chicken leftovers into the Instant Pot, then add the vegetable scraps and herbs.
Fill the Instant Pot with about 3 quarts of water; enough to cover the contents. Stir in the salt and the peppercorns.
Press the Sauté button and bring the liquid to a simmer. Let it simmer for about 10 minutes, skimming off any foam that collects at the top. (This doesn't always happen, so don't be alarmed if you don't have to skim any foam.)
After about 10 minutes, turn off the Sauté function. Lock the Instant Pot lid in place, set the valve to Sealing, and cook the content for 40 minutes on high pressure.
After 40 minutes, manually release the pressure.
Place a fine-mesh strainer over a large bowl or pot, and carefully dump the content of the Instant Pot over the strainer, letting the liquid collect in the bowl below. Discard the solids collected in the strainer.
Let the mixture cool. Once cooled, transfer the stock to freezer-friendly containers. Keep the stock in the fridge for up to five days, or in the freezer for up to six months.