const [isChecked, setIsChecked] = useState(false);

    const handleAllChecked = (e) =>{

        if (e.target.checked) {

            setIsChecked(true);

        }

        else{

            setIsChecked(false);

        }

    }

    // HTML code checkbox 

 <input

    onChange={(e) => {

    // add to list

    if (e.target.checked) {

        setFlatId([...flatId, e.target.value]);

    } 

    else {

        // remove from list

        setFlatId(flatId.filter((unChecked) => unChecked !== e.target.value));

        }

    }}

    defaultChecked={isChecked}

    value={flat.id}

    type="checkbox"

 />