Make sure the stainless steel insert is in your Instant Pot.
In a small bowl, mix the rub ingredients. Rub all over the pork roast. Cut the meat into 4 pieces.
Press "saute" setting on your Instant Pot. Wait 2 minutes, then add olive oil. Place meat in the Instant Pot. Let it sear on each side for 2 to 3 minutes. Remove onto a plate.
Add ¼ cup of water and deglaze the bottom of the pot (with a wooden spoon, scrape any cooked on bits). Add remaining water and apple cider vinegar.
Place pork back in the IP. Sprinkle chopped onion around and between the meat pieces.
Pour BBQ sauce over the meat, do not stir.
Close the lid, set the valve to "sealing" position. Make sure the IP is set to cook on HIGH pressure. Press "manual" setting, set timer to 45 minutes.
The IP will take 12 to 14 minutes to come to pressure. Once the timer is done, press "cancel/off" button and do not touch the valve. Let the IP release the pressure naturally. If you quickly release it, the meat will be tough.
Carefully open the lid away from your face. Remove the meat onto a plate and shred with two forks.
Reserve ½ cup of the liquid from the IP, discard the rest. Pour the sauce over pork just before serving.