Думаю, вам поможет следующий фрагмент.
const Ad = () => <div> ad item </div>;
const itemsArrays = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const firstSix = itemsArrays.splice(0, 6);
const List = () => {
let [topItems, setTopItems] = useState(firstSix);
let [bottomItems, setBottomItems] = useState(itemsArrays);
return (
<>
{topItems.map((item, index) => (
<div> {item.title} </div>
))}{" "}
<Ad />{" "}
{bottomItems.map((item, index) => (
<div> {item.title} </div>
))}{" "}
</>
);
};