In page.cs

ApplicationView.PreferredLaunchViewSize = new Size(1368, 912);
ApplicationView.PreferredLaunchWindowingMode = ApplicationViewWindowingMode.PreferredLaunchViewSize;

In page.cs

var view = ApplicationView.GetForCurrentView();
view.TryEnterFullScreenMode();

OnLaunched in App.xaml.cs

ApplicationViewTitleBar formattableTitleBar = ApplicationView.GetForCurrentView().TitleBar;
formattableTitleBar.ButtonBackgroundColor = Colors.Transparent;
CoreApplicationViewTitleBar coreTitleBar = CoreApplication.GetCurrentView().TitleBar;
coreTitleBar.ExtendViewIntoTitleBar = true;