Add the oil to your Instant Pot and press the sauté button. Add the onion and cook for 3-4 minutes. Turn off the sauté function when it's done.
Add the hot sauce, vinegar, Worcestershire sauce, and garlic powder to your pressure cooker. Give it a good stir.
Add the chicken and give it a stir so it's all nicely coated in the sauce.
Close the Instant Pot's lid, set the valve on "sealing", and cook on high pressure for 10 minutes. It'll take 5-10 minutes for it to reach pressure.
While the chicken is cooking, prep your lettuce and buns. Make the ranch dressing if you're using my ranch recipe.
Once the countdown has finished, let the pressure release naturally for 5 minutes, and then do a quick release for the remaining pressure.
Once the chicken's done, take it out of the Instant Pot. Add the butter to the Instant Pot, and while it's melting, shred the chicken using two forks. Add the chicken back into the Instant Pot and stir to coat with the sauce. Assemble sandwiches as desired.