Brown onions and pork: Set instant pot to sauté. Add butter and cook onions until softened. Push to one side and add chops to brown. Season with salt and pepper as they cook.
Add sauce: Switch off instant pot. Add beef stock and Worcestershire sauce, scraping the browned bits from the bottom of the instant pot.
Pressure cook: Close instant pot and set valve to sealing. Choose "pressure cook" for 8 minutes. After cooking time is up, do a natural pressure release for 5 minutes, then manually release remaining pressure and open.
Thicken: For a thicker sauce, remove chops form instant pot and cover to keep warm. Set instant pot to sauté and simmer sauce for a few minutes. If desired, add a slurry of arrowroot and water (or your preferred thickener).
Add cream: Switch off instant pot and let it cool down for a few seconds. Stir in sour cream. Serve sauce over chops.