Serve this flavorful slow-cooker chicken recipe over egg noodles, rice, or mashed potaotes. Make sure the mushrooms are submerged in liquid while cooking.
Sprinkle chicken with 1/4 teaspoon of the salt and 1/4 teaspoon of the black pepper. Place flour in a shallow dish; dredge chicken in flour, reserving any remaining flour. Heat a large well-seasoned cast-iron skillet over medium-high heat. Add oil to pan; swirl to coat. Add chicken to pan; cook 3 minutes on each side or until golden brown. Transfer chicken to a 6-quart Instant Pot®.
Add onion and next 3 ingredients (through garlic) to pan; coat vegetables with cooking spray. Cook, stirring constantly, 6 minutes or just until tender. Transfer onion mixture to cooker.
Coat mushrooms with cooking spray, and add to pan. Cook, stirring constantly, 5 minutes or until browned. Transfer mushrooms to cooker.
Combine reserved flour, remaining 1/4 teaspoon salt, remaining 1/4 teaspoon black pepper, broth, and paprika in a bowl; stir with a whisk. Add broth mixture to cooker. Close and lock the lid of the Instant Pot®. Turn the steam release handle to "Venting" position. Press [Slow Cook], and use [Adjust] to select "Less" mode. Press [-] or [+] to choose 3 hours cook time.
Remove chicken from cooker, and place on a serving platter. Skim fat from surface of cooking liquid. Stir sour cream into cooking liquid. Serve sauce with chicken, and sprinkle with parsley.