How to fix supportFragmentManager?

Im trying to put google maps into SupportMapFragment on my MainActivity file like these ways:

val mapFragment = supportFragmentManager.findFragmentById(R.id.map) as? SupportMapFragment
        mapFragment?.getMapAsync(this)

and

val mapFragment = supportFragmentManager
            .findFragmentById(R.id.map) as SupportMapFragment
        mapFragment.getMapAsync(this)

And modifying my content_main.xml like:

 <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:orientation="horizontal"
                android:gravity="center_vertical">
                <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="@string/app_name"
                    android:textColor="#FFFFFF"
                    style="@style/TextAppearance.AppCompat.Widget.ActionBar.Title"/>
            </LinearLayout>

and

<LinearLayout
                android:layout_width="fill_parent"
                android:layout_height="fill_parent"
                android:layout_weight="13"
                android:orientation="horizontal"
                android:gravity="center_vertical">
                <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="@string/app_name"
                    android:textColor="#FFFFFF"
                    style="@style/TextAppearance.AppCompat.Widget.ActionBar.Title"/>
            </LinearLayout>

but the application is working like the next way:

Any advice?

EDIT This is my Activity_Main.xml:

<include
        xmlns:tools="http://schemas.android.com/tools"
        android:name="com.google.android.gms.maps.SupportMapFragment"
        layout="@layout/content_main"
        android:id="@+id/map"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />

<!--<fragment xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:map="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/map"
        android:name="com.google.android.gms.maps.SupportMapFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />-->

ps. I removed the <fragment> tag to debug some parts.

I solved it; as the guys taugh me in the comments, I'm going to post for future references if someone has same situation:

val mapFragment = SupportMapFragment.newInstance()
        supportFragmentManager.beginTransaction().add(R.id.map, mapFragment)
            .commit()
        mapFragment.getMapAsync(this)

Thank you.