Select 'Saute' on the Instant Pot. Melt cooking fat (1 tbsp) in the pot. Season the stew beef (1 1/2 lb) with a little salt and pepper. Add half of the beef and cook until browned, 2-3 minutes, then flip and repeat until browned on all sides. Transfer meat to a plate and repeat with remaining cooking fat and beef. Press 'Cancel' when the second half of the meat has been browned. Return all meat to the Instant Pot.
Place diced yellow onion (1 medium), 1/2" cubed potatoes (1 lb), sliced carrots (3 medium), sliced celery (2 ribs), canned, diced tomatoes and their liquid (14 oz), beef broth (4 cups), minced garlic (4 cloves), dried thyme (1 tsp), and italian seasoning (1 tsp) in the Instant Pot. Stir, lock the lid into place, set the vent valve to the 'sealing' position, and cook on high pressure for 20 minutes.
Allow for 10 minutes of natural release before flipping the value to the 'venting' position to release any remaining pressure.
Press 'Cancel' then select the 'Saute' setting. Add the green beans (1 cup) and frozen peas (1 cup) and cook for 5-6 minutes or until tender. Season with additional salt and pepper to taste before serving.