Instant Pot Corned Beef

Place onion in bottom of a 6-quart Instant Pot. Place brisket on top and add seasoning packet. Pour in broth and seal lid. Set to pressure cook on high for 90 minutes.  Follow manufacturer's guide for quick release, then remove corned beef and onions from Instant Pot. Keep remaining cooking liquid inside Instant Pot. Cover beef and keep warm.  Add cabbage, potatoes, carrots, and oil to Instant Pot. Season with salt and pepper, then seal lid. Set to pressure cook on high for 4 minutes.  Follow manufacturer's guide for quick release, then remove lid and serve vegetables with corned beef. Garnish with parsley and spoon additional cooking liquid over beef, if desired.