Pour the apple cider vinegar, brown sugar, Worcestershire sauce, and liquid smoke (if using) into the Instant Pot liner. Stir to combine the sauce base.
Place the seasoned pork shoulder on the trivet inside the Instant Pot.
Secure the lid and set the vent to sealing.
Cook on High Pressure for 60 minutes.
Allow for a Natural Pressure Release (NPR) for at least 15 minutes before manually releasing any remaining pressure.
Carefully remove the pork and place it in a large bowl. Shred using two forks.
Pour off any excess liquid from the pot, leaving about 1/2 cup of the cooking liquid.
Return the shredded pork to the pot along with your BBQ sauce. Stir well to coat.