Android Studio - "android:windowFullscreen" is not working

Question

Im building my first android app atm so Im not that experienced. I tried to make my app fullscreen but it didnt work. (Used this example Fullscreen Activity in Android? ) Im already trying this for a while but I couldnt figure out whats wrong. Mayb anyone can help.

Theme.xml

    <resources xmlns:tools="http://schemas.android.com/tools">
    <resources xmlns:tools="http://schemas.android.com/tools">
        <!-- Base application theme. -->
        <style name="Theme.Trinkspiel_1" parent="Theme.MaterialComponents.Light.NoActionBar">
            <!-- Primary brand color. -->
            <item name="colorPrimary">@color/purple_500</item>
            <item name="colorPrimaryVariant">@color/black</item>
            <item name="colorOnPrimary">@color/black</item>
            <!-- Secondary brand color. -->
            <item name="colorSecondary">@color/teal_200</item>
            <item name="colorSecondaryVariant">@color/teal_700</item>
            <item name="colorOnSecondary">@color/black</item>
            <!-- Status bar color. -->
            <!-- Customize your theme here. -->
            <item name="android:windowNoTitle">true</item>
            <item name="android:windowActionBar">false</item>
            <item name="android:windowFullscreen">true</item>
        </style>
    </resources>

Masifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.trinkspiel_1">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_logo"
        android:label="@string/app_name"
        android:logo="@mipmap/ic_logo"
        android:supportsRtl="true"
        android:theme="@style/Theme.Trinkspiel_1">
        <activity
            android:name=".InfoActivity"
            android:exported="false" />
        <activity android:name=".categories.ActionActivity" />
        <activity android:name=".categories.ClassicActivity" />
        <activity
            android:name=".FinishActivity"
            android:exported="true" />
        <activity
            android:name=".categories.RuleActivity"
            android:exported="true" />
        <activity
            android:name=".categories.QuizzActivity"
            android:exported="true" />
        <activity android:name=".categories.RandomShotActivity" />
        <activity android:name=".categories.HotActivity" />
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <meta-data
            android:name="preloaded_fonts"
            android:resource="@array/preloaded_fonts" />
    </application>

</manifest>