Heat olive oil in a large skillet over medium heat. Add onion, bell pepper, and celery, cooking for 5–7 minutes until softened.
Stir in garlic and cook for 1 minute until fragrant.
Sprinkle flour over the vegetables and cook, stirring constantly, for 1–2 minutes until lightly golden.
Gradually whisk in chicken broth, followed by heavy cream, Creole seasoning, Worcestershire sauce, and cayenne pepper.
Bring the sauce to a gentle simmer, reduce heat to low, and cook for 5–7 minutes until slightly thickened. Season with salt and pepper.
Stir in butter if using, then gently place the red snapper fillets into the sauce. Cover and cook for 5–7 minutes, until the fish flakes easily.
Sprinkle with fresh parsley and serve Red Snapper with Creamy Creole Sauce immediately over cooked rice.