Flickering startup screen with Qml Window {...} on Android

[PowerNow]

Hi, I observe during the startup of my android (8,9,10) apps with Qt 5.12.1 a disturbing flickering shortly with the shell in the background. It happens at the handshake between Android and Qt.

Order of visibility

1. color defined in the manifest.xml
2. the shell in the background
3. the color of the Qml Window {...} item

Window {
    visible: true
    width: Screen.width
    height: Screen.height
    color: "green"
}

Manifest.xml

... android:theme="@android:style/Theme.Holo.Light.NoActionBar.Fullscreen" ...
... android:background="#ffffffff" ...

Similar to this
https://forums.expo.io/t/android-splashscreen-flicker-white-and-resize/24969

The flickering varies a little (transparent with visible shell or black) on my different smartphones LG G6, Samsung Tablet, Huawei Mate20.

The same behaviour shows up too on the Qt Example projects.

What I'm doing wrong? Is there a way to avoid this flickering?