Set Instant Pot to Sauté mode. Add 1 tablespoon neutral oil, covering bottom of Instant Pot insert, and warm oil until hot and shimmery.
When oil is hot, add 1 medium white onion (diced) and 3 cloves garlic (minced). Stir to incorporate onion and garlic into oil, then sauté 2 to 3 minutes or until ingredients are fragrant and softened.
Add 2 cups frozen corn kernels, 1 4-ounce can diced green chiles, 1 teaspoon cumin, 1 teaspoon chili powder, 1 teaspoon dried oregano, 2 15-ounce cans Great Northern beans, and 1 cup low-sodium chicken broth to Instant Pot. Stir well to incorporate all ingredients, making sure to scrape up any bits of onion or garlic that may have stuck to bottom of insert.
Place 1 pound boneless, skinless chicken breasts in Instant Pot.
Secure lid on Instant Pot with vent in Sealing position. Set Instant Pot to Manual High Pressure and set cook time to 20 minutes. Instant Pot will pressurize, then 20-minute cook time will begin.
After cook time ends, Natural Release pressure for 10 minutes. After 10 minutes, immediately Quick Release any remaining pressure, then carefully remove Instant Pot lid and set aside.
Transfer chicken breasts to cutting board, then, using 2 forks, shred chicken breasts into smaller pieces. When satisfied with shredded chicken, return chicken to Instant Pot.
Add ¼ cup full-fat cream cheese (at room temperature) and ½ cup full-fat sour cream (at room temperature) to Instant Pot. Stir until dairy products are melted and fully incorporated into chili.
Once cream cheese are sour cream have melted, taste chili. Season with salt and freshly cracked black pepper as desired and let chili rest 2 to 3 minutes.
When satisfied with flavor, portion chili into serving bowls. Top each serving with finely chopped cilantro, diced avocado, and a squeeze of fresh lime juice. Serve chili warm with tortilla chips and lime wedges to garnish.