Combine the flour, dried thyme or parsley, black pepper, salt, and, if using, the baking powder and baking soda in a mixing bowl. Form a well in the center and incorporate the beaten eggs, blending to form a dense dough. Introduce milk gradually if the dough requires moisture to bind.
Bring a generously salted pot of water to a rolling boil. Dip a spoon in the hot water, scoop out portions of dough roughly the size of a tablespoon, and drop them into the boiling water. Allow the dumplings to cook until they rise to the surface, signaling they are cooked through. Retrieve with a slotted spoon and set aside.
In a large sauté pan, melt 2 tablespoons of butter and cook the chopped onion until it becomes tender and translucent, approximately 8–10 minutes. Add the remaining butter along with the cabbage, stock, and garlic powder. Season with salt and pepper to taste, cover the pan, and let it simmer until the cabbage reaches a soft, stewed consistency.
Fold the prepared dumplings gently into the cabbage mixture, stirring to combine without breaking them. Sprinkle with freshly chopped parsley and adjust seasoning if needed before serving.