If you want to create a simple top bar in compose here is the code breakdown.
@Composable
fun SimpleTopBar(screenName:String) {
TopAppBar(
title = {
Text(text = screenName)
},
modifier = Modifier
.systemBarsPadding(), // This is equivalent to android:fitsSystemWindows="true" ,
backgroundColor = Color.Blue,
contentColor = Color.White,
)
}