要手动将焦点设置为focusable，可以使用FocusRequester，如下所示：

@Composable
fun FocusBox(text:String, requester: FocusRequester = FocusRequester()){
    var color by remember { mutableStateOf(Color.White) }
    Box(
        Modifier
            .focusRequester(requester)
            .onFocusChanged {
                color = if (it.isFocused) Color.Green else Color.White
            }
            .focusable()
            .border(2.dp, color)
    ) {
        Text(text = text,
            modifier = Modifier.padding(10.dp))
    }
}

Row(
    Modifier
        .background(Color.Yellow)
        .padding(10.dp)
) {
    val requester = FocusRequester()
    FocusBox("Box01", requester)
    LaunchedEffect(Unit) {
        requester.requestFocus()
    }
    Spacer(modifier = Modifier.padding(10.dp))
    FocusBox("Box02")
    Spacer(modifier = Modifier.padding(10.dp))
    FocusBox("Box03")
    Spacer(modifier = Modifier.padding(10.dp))
    FocusBox("Box04")
}

LaunchedEffect是一个副作用，当可组合的出现时，它只运行一次。