Season the beef stew meat with the salt, black pepper, and paprika, tossing to coat the pieces evenly.
Heat the olive oil in a large skillet over medium-high heat, then add the seasoned beef stew meat and sear for a few minutes, turning occasionally, until the edges are browned. Work in batches if needed to avoid crowding the pan.
Transfer the browned beef stew meat to the crock pot, leaving any drippings in the skillet.
Add the sliced onion and minced garlic to the same skillet and cook over medium heat for 2 to 3 minutes, stirring, until the onion starts to soften.
Stir in the sliced mushrooms and cook for another 2 to 3 minutes until they begin to release their moisture.
Sprinkle the all-purpose flour over the vegetables in the skillet and stir well to coat, cooking for about 1 minute to remove the raw flour taste.
Gradually pour in the beef broth while stirring, then add the Worcestershire sauce and Dijon mustard, stirring until a smooth sauce forms and begins to thicken slightly.
Pour the sauce and vegetables from the skillet over the beef stew meat in the crock pot, stirring gently to combine everything.
Cover the crock pot with the lid and cook on LOW for 6 to 7 hours, or on HIGH for about 3 to 4 hours, until the beef is very tender.
About 20 minutes before serving, cook the egg noodles according to the package directions, then drain them well.
Stir the sour cream into the crock pot until fully combined with the sauce, then taste and adjust seasoning if needed.
Serve the Crock Pot Beef Stroganoff over the cooked egg noodles and sprinkle with chopped fresh parsley if using.