Add chicken breasts, chicken broth, salt, and pepper to Instant Pot. Stir and place the lid on top with the vent sealed. Use the manual setting to cook on high for 10 minutes.
Once it is done cooking, allow to natural release for 5 minutes. Then shred chicken with forks or bear claws and drain broth.
In a bowl, add mayonnaise, dijon mustard, diced celery, diced red onion, salt, and pepper, and mix well.
Once the chicken has cooled add to the bowl. Blend well and refrigerate for at least 30 minutes prior to serving.
Notes
Note: Can be served immediately, but traditionally is served cold.