Press SAUTE on Instant Pot. Heat oil (or butter), add minced garlic and onions. Saute until they soften and turn translucent.
Add diced zucchini, vegetable broth (or water), and salt.
Close the lid securely, and turn the vent to "SEALING". Select the PRESSURE COOK/MANUAL (High Pressure) setting and set the cooking time to 5 minutes.
When the instant pot beeps, allow the pressure to release naturally for 10 minutes, then release any remaining pressure before removing the lid.
Puree the soup using an immersion blender until smooth. (Or transfer the mixture to a traditional blender in batches and puree until smooth). Adjust seasoning.
Lastly, add coconut milk or heavy cream, black pepper, and stir well. If you think the soup is too thick, you can add vegetable broth or coconut milk to the soup and Simmer for 2 minutes.
Creamy Zucchini soup is ready to serve.