How do you make an app-wide light/dark mode switch in XAML and C# (UWP)?

Question

I am trying to make a UWP app (in Visual Studio 2019) which has a NavigationView (Top). Each NavigationViewItem has a different page associated with it/written for it.

I am trying to put an app-wide dark mode toggle-switch (which switches the app's theme dynamically/on the spot/at runtime). The following is my code to do that, which also generates an error in an auto-generated file called App.g.i.cs:

// App.xaml.cs

/*
.
.
.
*/
using Windows.UI.Xaml;

// namespace AppName
// {
sealed partial class App : Application
{
    /*
     * Default/Auto-generated initial code
     */

    // `static` for inter-app usage/to use these functions in a different app C# file/class
    public static ApplicationTheme GetApplicationTheme()
    {
        return App.Current.RequestedTheme;
    }

    public static void SetApplicationTheme(ApplicationTheme applicationTheme)
    {
        App.Current.RequestedTheme = applicationTheme;
    }

    // Made this to try to remove the error, but failed
    public static bool IsDarkModeEnabled()
    {
        return GetApplicationTheme() == ApplicationTheme.Dark;
    }

    // This too was made as an attempt to remove the error, but failed as well
    public static void SwitchApplicationTheme()
    {
        if (IsDarkModeEnabled())
        {
            SetApplicationTheme(ApplicationTheme.Light);
        }
        else
        {
            SetApplicationTheme(ApplicationTheme.Dark);
        }
    }
}
// }

<!-- Settings.xaml -->

<!-- <Page Loaded="Page_Loaded"
           ...> -->
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="1*" />
            <RowDefinition Height="9*" />
        </Grid.RowDefinitions>

        <ToggleSwitch x:Name="DarkModeToggleSwitch"
                      Header="Dark mode"
                      Grid.Row="0"
                      Toggled="DarkModeToggleSwitch_Toggled" />
    </Grid>
<!-- </Page> -->

// Settings.xaml.cs

/*
.
.
.
*/
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;

// namespace AppName
// {
public sealed partial class Settings : Page
{
    /*
     * Default/Auto-generated initial code
     */

    private void Page_Loaded(object sender, RoutedEventArgs e)
    {
        DarkModeToggleSwitch.IsOn = App.IsDarkModeEnabled();
    }

    private void DarkModeToggleSwitch_Toggled(object sender, RoutedEventArgs e)
    {
        App.SwitchApplicationTheme();
    }
}
// }

The error is generated when -

• navigating to the Settings page (in system dark mode), and
• when clicking DarkModeToggleSwitch (in system light mode)

This makes me assume its because of toggle-switching programmatically to dark mode, and I don't understand why that is happening

This is the error raised in App.g.i.cs due to the above reasons: This is the elongated error:

Also, please let me know if there is a way to add RevealBrush to the default Settings icon button in the top NavigationView (because it is not used/enabled by default)

Please help me with this! Thank you!

PS: Any doubts regarding the question will be answered in comments or through question edits.