How to Make It
Select SAUTÉ setting on a programmable pressure multicooker (such as Instant Pot). Select HIGH temperature setting. Add oil, and allow to preheat. Add onion and garlic; cook, stirring often, until just browned, about 6 minutes. Add mushrooms; cook, stirring often, until liquid has been released from mushrooms, about 6 minutes. Stir in broth, salt, and pepper. Turn off cooker. Arrange green beans on top of mixture in cooker; do not stir.
Cover cooker with lid, and lock in place. Turn steam release handle to SEALING position. Select MANUAL/PRESSURE COOK setting. Select HIGH pressure for 1 minute. (It will take 5 to 6 minutes for cooker to come up to pressure before cooking begins.) Let the pressure release naturally for 2 minutes. Carefully turn steam release handle to VENTING position, and let steam fully escape (float valve will drop). (This will take 1 to 2 minutes.) Remove lid from cooker. Transfer green beans to a large serving bowl or dish.
Stir together heavy cream and flour in a bowl until smooth. Select SAUTÉ setting on cooker. Select HIGH temperature setting. Whisk heavy cream mixture into mushroom mixture in cooker. Cook, stirring often, until mixture thickens, about 4 minutes. Turn off cooker.
Spoon mushroom mixture over green beans in serving bowl; sprinkle with fried onions.