React onDrop is not firing

You must preventDefault() behavior of the dragover event like this:

onDragOver = (e) => {
    let event = e as Event;
    event.stopPropagation();
    event.preventDefault();
}

Preventing default behavior in the dragover event “indicates that element is a draggable location”, as seen in MDN docs here, here and here. Then the drop event will work.