Mix together garlic powder, onion powder, salt, pepper, and brown sugar in small bowl. Liberally rub spice mixture all over pork shoulder roast, being sure to coat all sides evenly and thoroughly.
Set Instant Pot to Sauté mode, then add butter to pot and let melt. Add pork roast to melted butter and sear approximately 3 minutes per side, until roast is nicely golden brown. Using tongs, transfer pork roast to cutting board and set aside.
If needed, add more butter or a small amount of neutral oil to Instant Pot. Add onions and garlic and cook 3 to 5 minutes or until softened.
Pour in white wine to deglaze pot and scrape any browned bits off bottom of pot. Let wine come to boil then cook 2 minutes.
Add broth, rosemary, carrots, potatoes, dijon mustard, and dried thyme. Stir well, then return pork roast to Instant Pot.
Secure lid on pot with vent in Sealing position. Set to Manual High Pressure for 30 minutes (see Notes). Once cook time is up, Natural Release pressure for 10 minutes, then carefully turn the vent to Venting position to release any remaining pressure and remove lid.
Remove pork shoulder, potatoes, and carrots from Instant Pot and set aside. In small bowl, mix together cornstarch and water until no lumps remain and slurry is smooth. Pour slurry into Instant Pot and set to Sauté. Simmer until gravy has thickened, then return pork and vegetables to pot. Spoon gravy over top of pork roast and serve warm with plenty of gravy.