In a large zip top bag, combine flour, salt, pepper, onion powder, and 1/2 teaspoon Italian seasoning. Add beef and shake to coat.
Set Instant Pot to SAUTE. Add oil and brown beef in batches on all sides. Transfer to a plate. (Optional but recommended.)
Add onions and garlic to pot; sauté 1-2 minutes. Add balsamic vinegar and tomato paste; stir to deglaze, about 1 minute.
Return beef to pot. Add potatoes, sweet potato, carrots, celery, Worcestershire sauce, remaining 2 teaspoons Italian seasoning, bay leaf, beef broth, and star anise (if using). Stir. Add water if needed to cover vegetables.
Cover and seal lid. Set to Manual/High Pressure for 20 minutes. Allow natural release for at least 15 minutes.
Optional Thickening: Make slurry with cornstarch and water. Set Instant Pot to SAUTE, bring stew to a boil, stir in slurry, and simmer until thickened.
Discard bay leaf and star anise. Adjust salt and pepper. Garnish with parsley and serve.