Turn on the saute mode on your Instant Pot and let it heat until it's hot. Put in the ground beef and onions and cook until the meat is browned. Drain off the grease. Make certain to deglaze the pot by putting in water or beef broth and scraping the bottom with a wooden spoon. Once done, turn off the saute mode.
Add in the Worcestershire sauce, garlic, pepper, paprika, and dry mustard. Put the pasta on top and press it down into the liquid. Top this with the mushrooms. DO NOT STIR. (you can add some salt if needed)
Put on the lid to the Instant Pot and set the valve to sealing. Turn to "manual" and cook for 6 minutes. Once done, quick release the pressure when the cycle is completed.
Add in the sour cream and stir. Put on the lid and let the sauce absorb some.