Use a pressure cooker's sauté function to cook the onion in olive oil until soft, about 5 minutes, before adding the garlic and Italian Bomba sauce.
Cook another 30-60 seconds until fragrant before turning off the sauté function. Add a few tablespoons of broth to deglaze the pot.
Once deglazed, add the marinara, remaining broth, Risoni, and frozen meatballs. Stir everything together and seal the Instant Pot. Pressure cook with high pressure for 5 minutes and vent immediately.
Top the finished meatballs and rice with the shredded cheese and use the broil function (Instant Pot Duo Crisp only) for 5 minutes to melt the cheese. If you don't have a broil function, just place the lid back on the pot to melt with residual heat or fold the cheese straight in.
Top with fresh parsley, parmesan, and red pepper flakes, if desired.