Press SAUTE button. Once heated up, add in ground beef, onion, and celery. Cook until beef is no longer pink and onion is translucent. Season with salt and pepper as desired.
Press CANCEL button so that it stops cooking the beef.
Add in the potatoes and carrots sprinkle the onion soup mix on top.
Pour the beef broth, tomato sauce, and diced tomatoes on top of the potatoes and carrots. Gently mix together.
Place the lid on top of the Instant pot. Move the valve to SEALING (not venting).
Press the MANUAL button and set timer for 8 minutes.
When the timer is done, allow the Instant Pot to do a natural release for at least 15 minutes (you can go longer if desired).
Move the valve to VENTING and release remaining pressure.
Remove the lid and mix in the cream of mushroom soup and frozen mixed vegetables. Let the stew sit for 3-5 minutes so that the vegetables can cook.
Dish into bowls and serve!