On 6-quart Instant Pot™, select SAUTE; adjust to normal. Melt butter in insert. Add mushrooms, onions, thyme, pepper and salt; cook 11 to 13 minutes or until mushrooms are lightly browned and onions soften. Select CANCEL. Stir in broth and soy sauce; continue to stir 30 to 60 seconds to remove browned bits from bottom of insert.