Make this soup how you like, either vegetarian or not. Embellish it with a hit of protein by adding a cup of either cooked chick peas or cooked shredded chicken when you add the spinach.
Set the Instant Pot to saute. Add the olive oil and when it's warm, add the onion. Saute until tender, but not browned, 4 to 5 minutes.
Add the garlic and saute 1 minute. Add the carrots, celery, fennel, cumin, rice, and broth. Stir and set the lid on the IP with the vent closed. Set to high pressure for 14 minutes.
After 14 minutes, allow natural pressure release for 10 minutes. Carefully open the vent to release the remaining pressure and remove the lid. Add the spinach, butter, 3 tablespoons lemon juice and 1 teaspoon salt (if your broth is NOT low sodium, you may want to scale back the salt). Stir well, taste, and add more lemon and salt if needed.
Note: The rice in any leftover soup will continue to absorb the broth. Feel free to add more broth (or even a little water) as needed, adjusting the lemon and salt as needed.