[рони]

gsdev99,
пока неизвестно, как формируется новое type, вариант такой

const widgets = [
    {
        type: "Title",
        data: {
            title: "title1",
            subTitle: "subTitle1"
        }
    },
    {
        type: "Title",
        data: {
            title: "title2",
            subTitle: "subTitle2"
        }
    },
    {
        type: "Title",
        data: {
            title: "title3",
            subTitle: "subTitle3"
        }
    },
    {
        type: "New",
        data: {
            title: "new title1",
            subTitle: "new subTitle1"
        }
    },
    {
        type: "New",
        data: {
            title: "new title2",
            subTitle: "new subTitle2"
        }
    },
    {
        type: "NewTitle",
        data: {
            title: "NewTitle title1",
            subTitle: "NewTitle subTitle1"
        }
    },
];

const create = arr => {
    const map = new Map;
    arr.forEach(o => {
        let {type, data} = o;
        //type = "Section" + type;
        if(map.has(type)) map.get(type).children.push(data);
        else map.set(type, {type, children : [data]})
    })
    return [...map.values()]
};
const widgetsTransform = create(widgets)
console.log(widgetsTransform)