In an Instant Pot, place chicken breasts in an even layer. Sprinkle with Kosher salt and cover with water. Secure the lid. Set the valve to 'seal'.
Set the Instant Pot to the 'Meat/Stew' or high pressure function to cook for 15 minutes. When the timer is done, carefully quick-release the pressure. Once the pressure is completely released, carefully open the lid. Drain the chicken, discarding the liquid, and transfer to a cutting board to shred using 2 forks. Set aside.
Preheat the oven to 400°F. Spray a 9-inch baking dish with nonstick spray and set aside.
Set the Instant Pot to the 'Sauté' function. Add the cream cheese, buffalo sauce, ranch dressing, and mozzarella cheese. Stir constantly until the cheese is melted and the sauce is smooth. Add the shredded chicken and stir until well coated. Season to taste.
Spread the buffalo chicken dip into the baking dish and sprinkle cheddar cheese over the top. Bake for 10 minutes, or until the cheese is bubbly.
Top with sliced green onions and blue cheese, if desired. Serve hot with tortilla chips and/or vegetables.