Using the Sauté function on your Instant Pot, melt the butter. Add the chopped onion, carrots, and celery and cook for 5 minutes, stirring occasionally, until the onion becomes soft and translucent. Stir in the minced garlic and cook for 1 more minute until fragrant.
Turn off the Sauté function. Pour in the chicken broth, using a wooden spoon to scrape up any browned bits from the bottom of the pot. Add the dried thyme, bay leaf, black pepper, and salt.
Place the whole chicken breasts into the pot, ensuring they are submerged in the broth. Secure the lid, set the valve to Sealing, and select Manual/Pressure Cook on High Pressure for 10 minutes.
Once the cooking time is complete, allow the pressure to release naturally for 10 minutes, then carefully perform a quick release for any remaining pressure. Unlock and remove the lid.
Transfer the cooked chicken breasts to a cutting board. Use two forks to shred the chicken into bite-sized pieces, then return all the shredded chicken to the pot.
Turn the Instant Pot to the Sauté function. Add the egg noodles to the simmering broth and cook for 5-7 minutes, stirring occasionally, until the noodles are tender but still firm to the bite (al dente).
Turn off the Instant Pot. Remove and discard the bay leaf. Stir in the fresh parsley and let the soup sit for 2 minutes to allow the flavors to meld. Taste and adjust seasoning with more salt and pepper if desired before serving.
