I’m working on an Android app (home project) written in Java. I’m a casual Android developer and in order to achieve full-screen functionality I applied the same steps I successfully used couple of years ago:

1. Change the theme:

<style name="Base.Theme.MyApp" parent="Theme.Material3.Light.NoActionBar">
    <item name = "android:windowActionBar">false</item>
    <item name = "android:windowNoTitle">true</item>
    <item name="android:windowFullscreen">true</item>
    <item name="android:windowLightStatusBar">false</item>

</style>

<style name="Theme.MyApp" parent="Base.Theme.MyApp" />

2. Main activity (extending FragmentActivity, the only activity I have since I’m using fragments):

protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         EdgeToEdge.enable(this); //apparently for API 35+ this is the only thing I need
 
         View decorView = getWindow().getDecorView();
         int uiOptions = View.SYSTEM_UI_FLAG_HIDE_NAVIGATION | View.SYSTEM_UI_FLAG_FULLSCREEN;
         decorView.setSystemUiVisibility(uiOptions);
 
         setContentView(R.layout.activity_main);
         ... }

The problem is, when testing this on API 34, my app is kind of full screen. There’s a thin black line on top where system bar should be. Also, Play Store gave me a warning I’m using deprecated methods for full screen view.
In order to resolve that I went through Google documentation, realized there are different methods for API versions 29 – 35 (my min SDK supported is 25) but apparently I couldn’t understand implementation properly as whenever I tried solutions from the Google docs – black line either stayed or app became full-screen with system bar drawn over top part of my app. I tried using insets and margins as Google docs suggested but it gave no results.
I was so desperate I even asked GTP for the solution and, obviously, I got speculative and non-working “solutions” and “ideas”.

Can you please help me with this? How to implement a proper full-screen support that works for API versions 29-35?

It’s incredible such a trivial every-day thing as showing app in full screen mode with no other elements on the screen is so elaborate and requires more code than setting a mere property of the activity hahah

EDIT:
This is the latest attempt I tried:

super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        EdgeToEdge.enable(this);

        Window window = getWindow();
        View decorView = getWindow().getDecorView();

        WindowCompat.setDecorFitsSystemWindows(window, false);
        WindowInsetsControllerCompat controllerCompat = new WindowInsetsControllerCompat(window, decorView);
        controllerCompat.hide(WindowInsetsCompat.Type.systemBars() | WindowInsetsCompat.Type.navigationBars());
        controllerCompat.setSystemBarsBehavior(WindowInsetsControllerCompat.BEHAVIOR_SHOW_TRANSIENT_BARS_BY_SWIPE);

and the result I get (top of the screen):

I have also removed anything from my themes.xml, theme parent is just Theme.Material3.Light.NoActionBar