To a food processor or blender, add 2 tablespoons olive oil, chopped onion, chopped garlic, tomatoes, ancho chile, chipotle pepper, adobo sauce, toasted pepitas, raisins, chocolate, salt, cumin and cinnamon; process until smooth.
In the meantime, set your Instant Pot to SAUTE.
Add 2 tablespoons olive oil to the Instant Pot to heat up.
Add chicken to the hot oil and brown chicken on both sides; about 2 to 3 minutes per side. You will want to do this in batches. Add more oil if needed.
Remove chicken from Instant Pot and deglaze the pot with chicken broth, scraping up the browned bits.
Return chicken to the Instant Pot.
Pour the blended sauce over the chicken.
Cover and seal the Instant Pot.
Cook on HIGH pressure for 8 minutes. If using chicken thighs, cook on HIGH pressure for 10 minutes.
Do a Quick Release. Use an instant read thermometer to check for doneness; temperature in the thickest part of the chicken should register at 165˚F. If not cooked through, just set the lid over the Instant Pot, cover and let stand for 2 to 3 minutes.
Open and remove chicken; transfer to a cutting board and shred.
In the meantime, select the SAUTE function on the Instant Pot and bring sauce to a simmer; let simmer for 8 minutes, or until thickened.
Stir shredded chicken back into the sauce.
Serve chicken over rice, nachos, tacos, etc.