Using sauté mode, heat oil in Instant Pot. Add mushrooms, onion powder, and salt and cook, stirring, until the mushrooms have released their liquid, or about 6 minutes. Add sherry and cook, stirring, until mostly evaporated, or about 1 minute. Stir in green beans and broth. Turn off sauté mode, and close and lock the lid and cook at high pressure for 3 minutes. Carefully release the pressure manually.