In a ziploc bag, add the beef along with salt, pepper and flour. Give the bag a good shake so that the beef is well coated in flour. If you choose not to use flour, then just season the meat with salt and pepper.
Press on SAUTE in the Instant Pot, and wait until it's hot. Add vegetable oil, and brown the beef cubes until they're browned but not cooked through. Remove from the Instant Pot and set aside. You might have to do this in batches as an overcrowded Instant Pot will make it difficult to brown the beef. Also feel free to skip this step and just add all the ingredients in the Instant Pot (without the flour), and pressure cook.
Deglaze the pot with water, then add the beef and the rest of the ingredients (potatoes, carrots, celery, onion, garlic, tomato paste, bay leaf, rosemary, and beef broth). Stir to combine, then cover with the lid.
Make sure that the vent is on sealing position, press on MANUAL or PRESSURE COOK, and set at 20 minutes. Allow the Instant Pot to come to pressure, then cook for 20 minutes. Once the cooking is finished, quickly release the steam.
Discard the rosemary sprig and bay leaf, and thicken the sauce (this is optional) by combining 2 tablespoons of cornstarch with 1 tablespoon of water and mixing this in the sauce. Set the Instant Pot on SAUTE, and as the stew starts to boil it will thicken. Garnish with freshly chopped parsley leaves and serve.