Heat olive oil in a skillet over medium heat. Brown the ground beef until fully cooked, breaking it apart with a spoon.
Add diced onion and garlic, then cook for 2–3 minutes until fragrant.
Drain excess grease if needed and transfer the beef mixture to the slow cooker.
Add chopped cabbage, diced tomatoes, tomato sauce, tomato paste, and beef broth.
Sprinkle in paprika, smoked paprika, Italian seasoning, salt, pepper, and red pepper flakes.
Stir everything together until well combined.
Cover and cook on LOW for 6 hours or HIGH for 3–4 hours until the cabbage is tender.
Stir before serving and garnish with fresh parsley if desired.