Why can't a mutableStateOf based data class update UI automatically in Android Studio?

Question

The var myData= mutableStateOf(MyData()) is based a data class, I think the UI component associated with it can be updated automatically when it changed.

I run the following code, I hope the text of Currect and Max on the UI can be updated automatically after I click "Start" button, but UI doesn't update, why?

class HandleMeter: ViewModel() {

    var temp= mutableStateOf(0)

    data class MyData(
        var current:Int=1,
        var max:Int=100
    ) 

    var myData= mutableStateOf(MyData())

    private var myJob: Job?=null

    private fun soundDbFlow(period: Long=100) = flow {
        while (true) {
            val data =(0..1000).random()
            emit(data)
            delay(period)
        }
    }

    fun calCurrentAsynNew() {
        myJob?.cancel()
        myJob = viewModelScope.launch(Dispatchers.IO) {
            soundDbFlow().collect {setMyData(it)}
        }
    }

    fun setMyData(input: Int) {
        temp.value=input    //Only for test

        myData.value.current = input
        if (input > myData.value.max) {
            myData.value.max = input
        }

       //myData.value= MyData(myData.value.current, myData.value.max)               Doesn't work
       //myData = mutableStateOf(MyData(myData.value.current, myData.value.max) )  Doesn't work
   }
}


@Composable
fun Greeting(handleMeter: HandleMeter) {

    var myData = handleMeter.myData

    Column(
        modifier = Modifier.fillMaxSize(),
        verticalArrangement = Arrangement.Center,
        horizontalAlignment = Alignment.CenterHorizontally
    ) {
        Text(text = "Current ${myData.value.current}")
        Text(text = "Max ${myData.value.max}")

        Button(
            modifier = Modifier.padding(vertical = 24.dp),
            onClick = { handleMeter.calCurrentAsynNew() }
        ) {
            Text("Start")
        }
    }
}