CollapsingToolbar with second toolbar instead of ImageView

I am trying to create an app with two toolbars on top and a specific collapsing/expanding behaviour on scrolling. See the mockup to get a deeper understanding of what I'm trying to achieve:

I already found this StackOverflow question that is trying to achieve for about the same, and the response is hinting towards using a CollapsingToolbarLayout and just using another <Toolbar /> instead of the usual <ImageView />, but I tried around and could not get any close to the desired result.

My current xml layout:

android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/mainContainer"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".MainActivity">

    

And the corresponding activity code:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
}

I am using a NoActionBar theme. If I run this configuration, there is just one Toolbar displayed, nothing can be seen from the second Toolbar or the CollapsingToolbarLayout.

Huge thanks to anyone who is trying to help.