How to iterate the array inside array of object in react js?

I am trying to iterate the data but it saying testData is not iterable.
This is my code –

const testData = details?.[0]?.one?.map((item) => {
    const labelTwo =
      item?.itemType === 'FIRST' ? 'newLabel' : 'oldLabel';
    return {
      label: details?.[0]?.one?.length > 1 ? labelTwo : 'labelOne',
      value: item?.value,
    };
  });
  const myData: Item[] = [
    ...testData,
    {
      label: 'first',
      value: 'firstValue',
    },
    isVisible && {
      label: 'second',
      value: 'secondValue',
    },
  ];
return (
  <>
    {myData?.map((item: Item) => {
      return (
       <div>
        <div>{item?.label}</div>
        <div>{item?.value}</div>
       </div>
      );
    }
  </>
)

Below in return when I am trying to iterate myData using map function then it is saying testData is not iterable.
Am I doing anything wrong ? what will be the best approach here to iterate the data