In a mixing bowl, combine the pineapple juice, white vinegar, minced garlic, adobo sauce, cumin, oregano, paprika, salt, black pepper, and chopped chipotle peppers (if using). Whisk until well combined.
Place the pork cubes into the Instant Pot and pour the marinade over the pork. Toss to ensure all the meat is well-coated with the marinade.
Seal the Instant Pot lid and set the valve to the sealing position. Select the 'Meat/Stew' setting and cook for 30 minutes.
Once the cooking time is complete, allow the Instant Pot to naturally release pressure for 15 minutes, then perform a quick release for any remaining pressure.
Remove the pork from the Instant Pot and set aside. If desired, use the sauté function to reduce the remaining liquid for 5-10 minutes, until slightly thickened.
Shred the pork with two forks or chop it into bite-sized pieces. Return the pork to the pot, mix with the reduced sauce, and stir well.
Warm the tortillas in a dry skillet or microwave until pliable.
To serve, fill each tortilla with the pork mixture, adding diced pineapple, chopped onions, and cilantro as desired.