Crisp the bacon in a medium skillet set over medium heat. Set aside crisped bacon and rendered fat.
In a small, dry pan set over medium-low heat, toast the star anise, bay leaf, cinnamon stick, and peppercorns until fragrant, about 3 minutes. Set aside.
Set the Instant Pot to “Sauté” mode. Add the oil and sugar to the insert of the pot and cook, stirring occasionally, until caramelized, 7 to 10 minutes. Add ginger, garlic, shallots, scallions, peppers, and fermented black bean sauce (if using). Cook until the aromatics have softened, and are starting to caramelize, another 5 to 7 minutes.
Add the rehydrated mushrooms and their water, toasted spices, crisped bacon, rendered fat, cooking wine, dark soy, and light soy. Stir to combine well, scraping up any browned bits. Add in whole chicken, breast side up, then pour in just enough water to barely cover the chicken. Set the Instant Pot to “Slow Cook,” and the timer for 1 hour and 30 minutes.
Tilting the chicken upwards, lift and drain off any excess sauce. Place chicken on a serving platter and set aside. Fish out the mushrooms, and plate them around the chicken.
While the chicken is resting, use a slotted spoon to strain out and discard the rest of the solids. Set the Instant Pot to “Sauté,” and reduce the liquid until slightly thickened, about 7 to 10 minutes. Stir in vinegar and half of the sesame oil, then transfer sauce to a gravy bowl for serving.
Brush the remaining tablespoon of sesame oil all over the bird.