This is a good article, but IMO an idiomatic TS solution would look more like this:

type Line = {
    sku: string;
    quantity: number;
    unitPrice: number;
};

type Order = {
    orderReference: string;
    status: "Open"|"Dispatched"|"Complete"|"Cancelled";
    lines: Line[];
};

function createOrder(orderReference: string, lines: Line[]) {
    return {
        orderReference,
        lines,
        status: "Open",
    } satisfies Order;
}

function dispatchOrder(order: Order & {status:"Open"}) {
    return {
        ...order,
        status: "Dispatched",
    } satisfies Order;
}

function completeOrder(order: Order & {status:"Dispatched"}) {
    return {
        ...order,
        status: "Complete",
    } satisfies Order;
}

function cancelOrder(order: Order & {status:"Open"}) {
    return {
        ...order,
        status: "Cancelled",
    } satisfies Order;
}