Cut the pork shoulder into a few chunks (working around the bone, if bone-in). Select the sauté function on the Instant Pot and brown the pork chunks on each side for 1-2 minutes to allow them to start browning.
Add all of the browned pork chunks to the Instant Pot with cider vinegar, chicken broth, salt, black pepper and crushed red pepper flakes if using. Close and seal the lid. Select Manual function on the Instant Pot and cook for 90 minutes.
Once the 90 minutes is up, allow the Instant Pot to depressurize naturally.
Shred the pork and toss with the cooking liquids. Serve with buns, cole slaw, extra sauce and enjoy!
*If you're using a bottled sauce, it will likely be packed with seasoning and possibly red pepper flakes. Be aware of the salt and seasoning in your bottled sauce before adding any additional salt, black pepper or red pepper flakes!