Turn the Instant Pot on the sauté setting and melt 2 tablespoons of butter. Add seasoned stew meat in small batches to the Instant Pot and brown all sides. As the meat browns remove it from the Instant Pot to a bowl until all the stew meat has been browned.
Sauté the vegetables and garlic in the Instant Pot. Return the browned stew meat along with any accumulated liquids, beef broth and fresh or dried herbs to the Instant Pot. Stir to combine. Place the Instant Pot lid on locking it into the closed position. Turn the pressure valve to the sealing position.
Press the manual button and set the timer to 18 minutes. Once the timer has alerted you the Instant Pot has finished pressure cooking allow it to naturally release steam for 2 minutes. Then quick release the remaining steam from the pressure cooker. Carefully remove the lid. Stir the 1 cup of Quick Cook Barley into the hot soup.
In a small bowl mix the cornstarch with the cool water and stir into the Instant Pot. Set the Instant Pot to the sauté function and bring to a boil stirring occasionally. Cook the beef barley soup for 10 minutes more or until the barley is soft and the soup broth has thickened.