In the instant pot, melt 2 tablespoons of the butter. Add in the onion, red bell pepper, garlic, and smoked sausage together until browned, about 5-7 minutes.
Stir in the flour, tomato paste, cajun seasoning, and parsley until smooth and well blended. Cook for about 1 minute.
Pour the mixture into the slow cooker.
Stir in the Cajun seasoning, parsley and water until combined.
Stir the rice, water, shellfish, and last 2 tablespoons of butter. Season with salt and pepper.
Seal and pressure cook for 5-6 minutes.
Serve immediately.