Stir broth and brown rice together in a multi-functional pressure cooker (such as Instant Pot) until rice is moistened. Add chicken, onion, carrot, celery, corn, garlic powder, onion powder, poultry seasoning, thyme, salt, and pepper. Close and lock the lid. Select high pressure and set the timer for 18 minutes. Allow 10 to 15 minutes for pressure to build.
Release pressure naturally, about 10 minutes. Carefully release remaining pressure using the quick-release method, 2 to 3 minutes. Remove the lid.
Stir half-and-half and cornstarch together in a small bowl; stir into the cooker along with frozen peas. Select Sauté function; cook, stirring constantly, until thickened and bubbly, 2 to 3 minutes.