Set the Instant Pot to the sauté mode. Add the ground beef (or turkey) and cook until browned, breaking it up with a wooden spoon, about 5-7 minutes. Drain excess fat if necessary.
Add diced onion and garlic to the pot and sauté for an additional 2-3 minutes until fragrant and the onion is translucent.
Stir in the diced bell peppers, diced tomatoes (with juices), beef or vegetable broth, uncooked rice, Italian seasoning, salt, black pepper, and crushed red pepper flakes (if using).
Close the lid of the Instant Pot and ensure the valve is set to sealing. Set the pot to cook on manual high pressure for 15 minutes.
Once the cooking time is complete, carefully perform a quick release of the pressure. After the steam has stopped, open the lid.
Stir in the drained kidney beans and let the soup sit for about 5 minutes to heat the beans through. Adjust seasoning if necessary.
Serve the soup hot, garnished with fresh parsley or cilantro if desired.