Sample project for this issue
In core-splashcreen-1.0.0-rc01, Theme.Splashscreen set android:windowLayoutInDisplayCutoutMode param is set to shortEdge. This flag value is kept after changing to the postSplashScreenTheme which is a surprising behavior.
A workaround is to set back android:windowLayoutInDisplayCutoutMode to default in the postSplashScreenTheme.
This also affects some other attributes like android:enforceNavigationBarContrast.