Press the Sauté button on the Instant Pot® and heat oil. Add flour and cook, stirring constantly, until flour is medium brown in color, about 15 minutes.
Add celery, onion, green pepper, garlic, and tomatoes and cook, stirring constantly, until the vegetables are tender, about 8 minutes. Add thyme, cayenne, bay leaves, filé, Worcestershire sauce, and stock and stir well, making sure nothing is stuck to the bottom of the pot, then add sausage. Press the Cancel button.
Close lid and set steam release to Sealing, then press the Manual button and adjust cook time to 8 minutes. When the timer beeps, quick release the pressure. Open lid and stir in shrimp, salt, and black pepper. Press the Cancel button, then press the Sauté button and cook for 8 minutes, or until shrimp are cooked through. Discard bay leaves. Serve hot over rice.