In a medium skillet, heat the oil over medium heat until shimmering. Add the onion and cook, stirring until lightly browned, about 5 minutes. Add the cabbage and cook until it begins to wilt, about 5 minutes. Add the apple, dried fruit, vinegar, sugar, a pinch each of salt and pepper, and 1/2 c water and bring to a boil. Cover partially and simmer over medium-low heat until cabbage is tender and liquid has evaporated, 10–12 minutes. Stir in the butter and season with salt to taste.