Turn Instant Pot to the saute setting. Add the olive oil and then the onions, carrots, parsnips, and celery. Saute for about 3 minutes until onion is translucent.
Add the garlic, fresh parsley, thyme, white pepper, and salt to the Instant Pot and stir. Then add the fresh lemon juice, chicken stock, and water.
Next, carefully place the chicken into the pot. Put the cover on the Instant Pot and seal it. Turn it to the "soup" setting and cook for 5 minutes for boneless chicken breasts and 7 minutes for chicken on the bone. Then do the 10-minute natural release method (refer to the instruction manual if needed). After that, carefully unseal and vent the soup. When it stops steaming completely unlock the lid and remove it from the pot.
Carefully take out the chicken and transfer it to a cutting board. Shred with two forks and then return it to the pot. Season the soup with additional salt and fresh lemon juice to taste. Garnish with additional parsley.
(If you want noodles in your soup, cook them separately, al dente according to package directions while the soup is cooking. Then drain and add to the bowls before ladling over the prepared soup).