Turn your Instant Pot to sauté. Allow it to heat up, which it does very quickly. Then, add your butter and olive oil. Sauté onion and garlic in the fats until nice and golden brown.
Turn your Instant Pot back on sauté, add renaming olive oil and butter and brown the meatballs. Remove to a plate. Add the water and 1/2 cup spaghetti sauce and stir well.
Add your spaghetti noodles over the sauce, top with meatballs and another 1 1/2 cups of sauce. Turn the Instant Pot on for 6 minutes, and release pressure quickly when it is done cooking. Serve immediately and enjoy!