Place chicken in the Instant Pot. Cut onion in half; set half aside. Cut remaining half into wedges; place on top of chicken.
Cut 1 stalk of celery in half; add to pot with chicken. Add bay leaf to pot.
Slowly pour broth over all in the pot.
Secure the lid on the pot. Close the pressure-release valve. Select Poultry and adjust to more. When cooking is complete, use a natural release to depressurize. Press cancel.
Meanwhile, chop reserved red onion half. Thinly slice remaining 2 stalks celery. Set aside.
Once pressure is released from the pot, transfer the chicken to a large cutting board; set aside.
Use a slotted spoon to remove and discard onion wedges, celery stalk, and bay leaf from liquid in pot. If desired, strain liquid in pot through a fine-mesh sieve; return liquid to pot if strained.
Skim fat from top of liquid in pot if desired. Add chopped onion, sliced celery, carrots, sweet pepper, noodles, garlic, salt, thyme, sage, and black pepper to pot.
Secure the lid on the pot. Close the pressure-release valve. Select manual and cook at high pressure for 2 minutes. When cooking is complete, use a quick release to depressurize. Press cancel.
When chicken is cool enough to handle, remove meat from bones. Discard bones and skin. Cut meat into bite-size pieces. Add chicken to soup in the pot.
Select sauté and adjust to normal. Cook, uncovered, for 1 to 2 minutes or until soup is heated through. Press cancel.
Stir in spinach and lemon juice just before serving.
Asian Chicken Noodle Soup
Prepare as directed except substitute 8 ounces rice noodles for the egg noodles, substitute 2 tablespoons reduced-sodium soy sauce for the salt, substitute 3 tablespoons to 4 tablespoons rice vinegar for the lemon juice, substitute shredded napa cabbage for the spinach, and substitute 2 tablespoons finely chopped fresh ginger for the dried thyme.