Turn Instant Pot to saute. Once the pot is hot, spray the bottom with cooking spray (or add a little oil), and add ground beef. Brown the meat, breaking it into small pieces as it cooks, and season it with salt and pepper. Remove any excess grease.
Add onion, garlic and sliced mushrooms and saute for 1 minute.
Add the flour, homemade or canned cream of mushroom soup, beef broth, and noodles and stir to combine.
Secure instant pot lid, and turn valve to sealed position. Cook on Manual Setting or High Pressure Setting for 2 minutes.
When pressure cooking is complete, use a quick release. (If liquid sprays from the knob, close knob, wait 30 seconds then release pressure again. You may also turn knob half way so only a small amount of steam is being released.)
Carefully remove the lid and stir mixture. Allow the mixture to cool for a few minutes, then stir in sour cream, parsley, additional salt and pepper to taste.