Whisk flour, garlic salt, and black pepper together in a small bowl; pour into a large resealable plastic bag. Place stew beef in bag, seal the bag, and shake to coat beef to coat completely.

Heat olive oil in a large skillet over medium-high heat; saute coated beef in hot oil until browned on all sides, about 10 minutes. Stir onion into beef; saute until onion is softened, 5 to 7 minutes. Pour beef and onions into a slow cooker.

Stir beef broth, red wine, and Worcestershire sauce together in a bowl. Pour broth mixture into the same skillet and bring to a boil while scraping the browned bits of food off of the bottom of the skillet with a wooden spoon. Transfer broth mixture to the slow cooker.

Mix potatoes, carrots, celery, garlic, bay leaves, beef stew seasoning mix, and paprika into beef mixture.

Cook on High for 1 hour. Reduce heat to Low and cook until meat is tender, 6 to 7 hours.