Turn on saute mode. When hot, add half the oil and the shrimp. Cook for 2 minutes, stirring occasionally. Transfer to a plate.
Add the sausage and cook for 2-3 minutes, stirring occasionally. Transfer to the plate and blot with a paper towel to remove oil, if necessary.
Season the chicken with salt and pepper. Add the remaining oil to the inner pot and pour in the chicken, bell pepper, onion, and celery. Cook, stirring occasionally, until the onion is translucent, about 3 minutes. Turn off saute mode. Add the garlic and cook for 30 seconds until fragrant.
Add the chicken broth to the pot and deglaze the bottom of the pot. Add the crushed tomatoes, tomato paste, Cajun seasoning, and rice. Stir all together.
Lock the lid. Press the Pressure Cook or Manual button and cook on high for 8 minutes. Allow for a natural pressure release for 5 minutes, then manually release the remaining pressure.
Stir the rice mixture, then stir in the shrimp and sausage. Replace the Instant Pot lid and allow the ingredients to heat through for 5 minutes on Keep Warm mode.