[Vuejs]-Why props default is not working when I'm trying to use a default title when no props are passed?

you have to rearrange your props:

export default {
  props: {
    section: {
      type: Object,
      default: () => {
        type: "section",
        title: "Introduction Props",
        desc: "",
        children: [
          {
            type: "lecture",
            title: "Introduction",
          }
        ]
      }
    },
};