Does anyone know how fake/pass navController to make a preview for BottomNavigation?

The alternative is to factor out the composable to accept simple values and lambdas

@Composable fun BottomNavigation(navController: NavController) {
    val currentDestination by navController.observeDestinationAsState()
    BottomNavigation(currentDestination, navController::navigate)
}

@Composable fun BottomNavigation(destination: String, navigate: (String) -> Unit) { ... }

and you can use the second composable for previews

Which is precisely what our docs say: https://developer.android.com/jetpack/compose/navigation#testing