Set the Instant Pot to the "Sauté" function. Add olive oil and butter, letting the butter melt. Sauté the onion until softened, about 3 minutes, then add garlic and cook for 1 more minute. Add the beef, season with salt and pepper, and cook until browned on all sides, about 5 minutes.

Stir in the mushrooms, paprika, and Dijon mustard, cooking for 2 minutes until mushrooms release some moisture.

Pour in the beef broth and Worcestershire sauce, scraping the bottom of the pot to deglaze any browned bits (this prevents the burn warning). Add the egg noodles, ensuring they are submerged in the liquid. Turn off "Sauté" mode, secure the lid, and set to "Pressure Cook" (or Manual) for 8 minutes.

Once the cooking cycle is complete, carefully perform a quick release by turning the venting knob. Open the lid, giving everything a gentle stir.

In a small bowl, mix sour cream with flour (if using) to prevent lumps. Stir it into the pot until the sauce is creamy and thickened. Adjust seasoning with additional salt and pepper as needed.

Ladle the stroganoff into bowls or over a plate of wide egg noodles, mashed potatoes, or rice. Garnish with fresh parsley or Parmesan cheese if desired.