Add oil to a large pot over medium heat. Add in onions and garlic and sauté for 5 minutes, stirring occasionally.
Add in cabbage, potatoes, carrots, celery, dijon mustard, 1 teaspoon of salt and pepper. Stir well and cook for 5-7 minutes, until the vegetables start to soften.
Add the remaining vegetable broth to the pot with the apple cider vinegar. Increase heat to high and bring the soup to a boil. Reduce heat to low, cover and simmer for 20 minutes.
In a small bowl, whisk together the ¼ cup of vegetable broth with the flour until smooth. Add to the soup and stir well.
Add the navy beans and dill and cook for an additional 10-15 minutes, until the soup is slightly thickened. Serve warm.