1. Heat the olive oil on the Instant Pot's Sauté setting. Cook the onion, carrot, celery, and garlic until tender, about 3-5 minutes. Stir in the vegetable broth, butternut squash, apple, nutmeg, cinnamon, thyme, rosemary, salt, pepper, and nutmeg (if using).
2. Seal the Instant Pot and set it to high pressure. Cook for 10 minutes, then do a quick pressure release.
3. Puree the soup using an immersion blender until smooth. If you don't have an immersion blender, allow the soup to cool slightly, then transfer it to a regular blender and blend until smooth.
4. Serve the soup warm in bowls.