Heat the Instant Pot on Saute mode (high setting). Add the oil. When hot, add the onions. Saute until softened, about 3 minutes.
Add the bell pepper and celery. Saute for 3 more minutes.
Add chicken and sausage. Saute for 3 minutes. Turn off saute mode.
Add the salt, Creole seasoning, cayenne pepper, and chicken broth.
Stir and deglaze the bottom of the pot.
Pour the tomatoes on top and press them down to submerge, but don’t stir them in.
Secure the lid and set the vent to sealing (if necessary for your model).
Set to cook on high pressure for 4 minutes. When the time is up, allow a 5-minute natural pressure release, then carefully release any remaining pressure. Remove the lid.
Stir in the shrimp and Gumbo file and put the lid back on for 6 minutes (on Keep Warm). This will cook the shrimp and slightly thicken the gumbo.
Remove the lid, stir, and serve over rice.