You cant have scrolling effects in Toolbar. So AppBarLayout is used, see below images, you can achieve by using only AppBarLayout.

Toolbar is just an usual View and it may be placed anywhere you want, even few in one XML. AppBarLayout is used to wrap Toolbar (or other View, e.g. TabLayout) and add some scroll-behavior change possibilities, when placed above some scrolling container like ScrollView or RecyclerView (you probably want to use Nested versions then)

check out nested classes listed in summary in on top of AppBarLayout doc – all related to scrolling (e.g. OnOffsetChangedListener or ScrollingViewBehavior)

The Code A is from the project architecture samples, the toolbar is wrapped with AppBarLayout.

I remove AppBarLayout and get Code B, and Code B works well just like Code A.

Must Toolbar be wrapped with AppBarLayout in Android Studio?

Code A (tasks_act.xml)

<androidx.drawerlayout.widget.DrawerLayout
    xmlns_android="http://schemas.android.com/apk/res/android"
    xmlns_app="http://schemas.android.com/apk/res-auto"
    xmlns_tools="http://schemas.android.com/tools"
    android_id="@+id/drawer_layout"
    android_layout_width="match_parent"
    android_layout_height="match_parent"
    tools_context=".tasks.TasksActivity"
    tools_openDrawer="start">

    <LinearLayout
        android_layout_width="match_parent"
        android_layout_height="match_parent"
        android_orientation="vertical">

        <com.google.android.material.appbar.AppBarLayout
            android_layout_width="match_parent"
            android_layout_height="wrap_content">

            <androidx.appcompat.widget.Toolbar
                android_id="@+id/toolbar"
                android_layout_width="match_parent"
                android_layout_height="wrap_content"
                android_minHeight="?attr/actionBarSize"
                android_theme="@style/Toolbar"
                app_popupTheme="@style/ThemeOverlay.AppCompat.Light" />
        </com.google.android.material.appbar.AppBarLayout>

        <fragment
            android_id="@+id/nav_host_fragment"
            android_name="androidx.navigation.fragment.NavHostFragment"
            android_layout_width="match_parent"
            android_layout_height="match_parent"

            app_defaultNavHost="true"
            app_navGraph="@navigation/nav_graph" />

    </LinearLayout>

    <!-- Navigation Drawer -->
    <com.google.android.material.navigation.NavigationView
        android_id="@+id/nav_view"
        android_layout_width="wrap_content"
        android_layout_height="match_parent"
        android_layout_gravity="start"
        android_fitsSystemWindows="true"
        app_headerLayout="@layout/nav_header"
        app_itemIconTint="@drawable/drawer_item_color"
        app_itemTextColor="@drawable/drawer_item_color"
        app_menu="@menu/drawer_actions" />

</androidx.drawerlayout.widget.DrawerLayout>

Code B (tasks_act.xml)

<androidx.drawerlayout.widget.DrawerLayout
    xmlns_android="http://schemas.android.com/apk/res/android"
    xmlns_app="http://schemas.android.com/apk/res-auto"
    xmlns_tools="http://schemas.android.com/tools"
    android_id="@+id/drawer_layout"
    android_layout_width="match_parent"
    android_layout_height="match_parent"
    tools_context=".tasks.TasksActivity"
    tools_openDrawer="start">

    <LinearLayout
        android_layout_width="match_parent"
        android_layout_height="match_parent"
        android_orientation="vertical">

       <androidx.appcompat.widget.Toolbar
           android_id="@+id/toolbar"
           android_layout_width="match_parent"
           android_layout_height="wrap_content"
           android_minHeight="?attr/actionBarSize"
           android_theme="@style/Toolbar"
           app_popupTheme="@style/ThemeOverlay.AppCompat.Light" />
     

        <fragment
            android_id="@+id/nav_host_fragment"
            android_name="androidx.navigation.fragment.NavHostFragment"
            android_layout_width="match_parent"
            android_layout_height="match_parent"

            app_defaultNavHost="true"
            app_navGraph="@navigation/nav_graph" />

    </LinearLayout>

    <!-- Navigation Drawer -->
    <com.google.android.material.navigation.NavigationView
        android_id="@+id/nav_view"
        android_layout_width="wrap_content"
        android_layout_height="match_parent"
        android_layout_gravity="start"
        android_fitsSystemWindows="true"
        app_headerLayout="@layout/nav_header"
        app_itemIconTint="@drawable/drawer_item_color"
        app_itemTextColor="@drawable/drawer_item_color"
        app_menu="@menu/drawer_actions" />

</androidx.drawerlayout.widget.DrawerLayout>