Set Instant Pot to sauté and add oil to pot once hot.
Cut pork shoulder into smaller chunks and sauté on each side until browned. You will need to do this in 2-3 batches.
Once all pieces of pork have been seared, turn off the sauté function by clicking the keep warm/cancel button.
All in all remaining ingredients (including all pork pieces) to the pot and lock the lid.
Press the Meat/Stew button and set manual for 30 minutes.
Let the pot release naturally, this should take approx 20 minutes.
Once the pot has released all pressure, take the Carnitas out of the pot with a slotted spoon onto a baking sheet with foil. Take some of the juice from the pot and pour over carnitas to retain the moisture.
Set the oven to broil and place the baking sheet with the carnitas and juice in the oven and bake until edges are crispy, just under 5 minutes. Make sure you check so they don't burn!
Take out of the oven and serve in warmed tortillas. Top with fresh onions and cilantro and some sliced fresh mango or avocado if desired. Make sure you squeeze some fresh lime on top!