Turn the Instant Pot on sautee, high. Add the oil and brown the ground beef. Drain off any fat and liquid.
Still on sautee, add the onions and garlic. Cook an addition 2-3 minutes or until onions are translucent.
Add the beef broth, thyme, mushrooms, salt and pepper. Turn the Instant Pot onto Pressure, High, and set it for 6 minutes. Lock it up. When the time is up, let it release naturally for 3 minutes, then manual release and open the pot.
Remove about 1/2 cup of the cooking liquid. Add that to the sour cream, tempering it. Once the beef stroganoff has stopped bubbling, add the sour cream and broth mixture to the beef and mix well.
Season with salt and pepper, and thicken with 1/4 tsp of xanthan gum if desired. Serve and enjoy!
Please note: Xanthum gum thickens up as it sits, so mix it in and let it stand for a few minutes before serving. Do not add too much xanthum gum!