Combine the garlic, soy sauce, and peppercorns in a non-reactive bowl or large freezer bag. Add the chicken pieces. Marinate for 3 hours or up to one day. Note: This step is optional. If you don't have the time, you can combine the marinade and add directly to the Instant Pot.
When ready to cook, add the marinade plus the vinegar and bay leaves to the Instant Pot. Nestle the chicken thighs into the pan. Bring the liquid to a boil on Saute mode, then turn off the machine and set it to Pressure Cook for 8 minutes.
After the cook time is over, allow the machine to naturally release pressure for 5 minutes, then finish with a quick manual release. Remove the chicken from the pot.
Press the Saute setting again and return the sauce to a boil. Add the sugar and stir to combine. While occasionally turning and basting the chicken, continue boiling the sauce, uncovered, until it is reduced by half and slightly thickened, 5–7 minutes.
Serve with steamed white rice.