Combine the ingredients in the Instant Pot. Add the chicken thighs, sea salt, ground black pepper, and olive oil to the bowl of an Instant Pot. Stir to coat the chicken in the olive oil and seasoning. Add the onion, garlic, and chicken broth and stir to mix.
Cook. Seal the Instant Pot and set it to cook on high pressure for 10 minutes. When the cook time is up, allow the pressure to naturally release.
Shred. Using a slotted spoon, transfer the chicken from the pressure cooker to a cutting board. Shred the chicken with two forks and set it aside. Discard everything else.
To assemble and bake
Prep. Preheat the oven to 350˚F.
Make the creamy layer. In a large mixing bowl, whisk together the whipped cream cheese, sour cream, and cottage cheese until well incorporated. Add the condensed cream of chicken soup and mix to combine.
Add the remaining ingredients. To the mixing bowl, add the cheese, the shredded chicken, salt, black pepper, garlic powder, onion powder, and dried oregano. Stir to combine. Transfer the cheesy chicken mixture to a casserole dish.
Make the topping. In a separate bowl, combine the crushed Ritz crackers and the unsalted butter and mix to combine. Evenly distribute the Ritz cracker mixture over the contents of the casserole dish.
Bake. Transfer the casserole dish to the oven and bake the casserole for 45 minutes.
Finish and serve. Remove the chicken casserole from the oven and let it rest for 10 minutes. Garnish with finely chopped scallion greens over the top and serve.