jetpack compose - Update state of another function variable

MainActivity.kt

package com.cfsuman.jetpackcompose

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.activity.compose.setContent
import androidx.compose.foundation.background
import androidx.compose.foundation.layout.*
import androidx.compose.foundation.shape.CircleShape
import androidx.compose.material.*
import androidx.compose.runtime.*
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.material.Text
import androidx.compose.material.TopAppBar
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clip
import androidx.compose.ui.text.font.FontWeight
import androidx.compose.ui.unit.dp


class MainActivity : AppCompatActivity() {
    @ExperimentalMaterialApi
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            GetScaffold()
        }
    }


    @ExperimentalMaterialApi
    @Composable
    fun GetScaffold(){
        var favCounter = remember {mutableStateOf(0)}

        Scaffold(
            topBar = { TopAppBarContent(favCounter) },
            content = {MainContent(favCounter)},
            backgroundColor = Color(0xFFEDEAE0)
        )
    }


    @ExperimentalMaterialApi
    @Composable
    fun TopAppBarContent(favCounter: MutableState<Int>) {
        TopAppBar(
            title = { Text(text = "Compose - Update state")},
            backgroundColor = Color(0xFFC0E8D5),
            actions = {
                Box(modifier = Modifier
                    .size(36.dp)
                    .clip(CircleShape)
                    .background(Color(0xFFF0FFFF))
                    .padding(8.dp),
                    contentAlignment = Alignment.Center
                ) {
                    Text(
                        text = "${favCounter.value}",
                        fontWeight = FontWeight.Bold
                    )
                }
                Spacer(modifier = Modifier.requiredWidth(12.dp))
            }
        )
    }


    @Composable
    fun MainContent(favCounter: MutableState<Int>){
        Box(
            modifier = Modifier.fillMaxSize(),
            contentAlignment = Alignment.Center
        ){
            Column(
                modifier = Modifier
                    .wrapContentSize(Alignment.Center)
                    .padding(24.dp),
                horizontalAlignment = Alignment.CenterHorizontally,
                verticalArrangement = Arrangement.spacedBy(12.dp)
            ) {
                Text(
                    text = "Update state of another function variable",
                    style = MaterialTheme.typography.h6
                )
                Button(
                    onClick = {
                        favCounter.value++
                    }
                ) {
                    Text(text ="Update State")
                }
            }
        }
    }


    @Preview
    @Composable
    fun ComposablePreview(){
        //GetScaffold()
    }
}