Can't update state inside useEffect

Question

I have a state,

const [weekdays, setWeekdays] = useState([{
    day: 'S',
    fullName: 'Sunday',
    select: false
},
{
    day: 'M',
    fullName: 'Monday',
    select: false
},
{
    day: 'T',
    fullName: 'Tuesday',
    select: false
},
{
    day: 'W',
    fullName: 'Wednesday',
    select: false
},
{
    day: 'T',
    fullName: 'Thursday',
    select: false
},
{
    day: 'F',
    fullName: 'Friday',
    select: false
},
{
    day: 'S',
    fullName: 'Saturday',
    select: false
    }])

I have newData,

    const newData=['Monday', 'Wednesday', 'Thursday']

I want to update that weekDays state to select: true for those days which are present in newData and others remains same.

I am trying in this way,I know this is not the correct way to update state,

    useEffect(() => {
    {
        if (data?.length > 0) {
            
            setWeekdays(weekdays=>([...weekdays,data]))
        }
    }
}, [data]);

If any one knows the answer then suggest me,How to achive this?

Thanks in advance...