Using highest Sauté function, heat oil in Instant Pot until shimmering. Add onions and salt and cook until onions are ¬softened, about 5 minutes. Stir in ginger, coriander, fennel, and cinnamon and cook until fragrant, about 30 seconds. Stir in broth, water, carrots, and baking soda.
Lock lid in place and close pressure release valve. Select Pressure Cook function and cook for 3 minutes. Turn off Instant Pot and quick-release pressure. Carefully remove lid, allowing steam to escape away from you.
Working in batches, process soup in blender until smooth, 1 to 2 minutes. Return processed soup to Instant Pot and bring to simmer using highest Sauté function. Season with salt and pepper to taste. Drizzle individual portions with pomegranate molasses and top with yogurt, hazelnuts, and cilantro before serving.