在现有.NET 6项目集成AvaloniaUI时遇窗口系统未配置错误

我正尝试在现有.NET 6项目中使用AvaloniaUI，但未找到相关集成指引，仅能找到创建新项目的教程。我看到大量官方示例使用如下入口代码：

class Program
{
    // Initialization code. Don't use any Avalonia, third-party APIs or any
    // SynchronizationContext-reliant code before AppMain is called: things aren't initialized
    // yet and stuff might break.
    [STAThread]
    public static void Main(string[] args) => BuildAvaloniaApp()
        .StartWithClassicDesktopLifetime(args);

    // Avalonia configuration, don't remove; also used by visual designer.
    public static AppBuilder BuildAvaloniaApp()
        => AppBuilder.Configure<App>()
            .UsePlatformDetect()
            .WithInterFont()
            .LogToTrace();
}

但我的项目中没有UsePlatformDetect()方法，于是尝试用UseStandardRuntimePlatformSubsystem()替代，却触发以下错误：

Unhandled exception. System.InvalidOperationException: No windowing system configured.
at Avalonia.AppBuilder.Setup()

我的入口代码：

internal class Program
{
    // Initialization code. Don't use any Avalonia, third-party APIs or any
    // SynchronizationContext-reliant code before AppMain is called: things aren't initialized
    // yet and stuff might break.
    [STAThread]
    public static void Main(string[] args)
    {
        BuildAvaloniaApp()
            .StartWithClassicDesktopLifetime(args);
    }

    // Avalonia configuration, don't remove; also used by visual designer.
    public static AppBuilder BuildAvaloniaApp()
        => AppBuilder.Configure<Main>()
            .UseStandardRuntimePlatformSubsystem()
            .LogToTrace();
}

我的主应用类（不打算使用XML特性）：

internal class Main : Application
{
    public override void OnFrameworkInitializationCompleted()
    {
        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
        {
            desktop.MainWindow = new MainWindow();
        }
    }
}

主窗口类：

internal class MainWindow : Window
{
    private TextBox imageLocation;

    public MainWindow()
    {...}
}

内容的提问来源于stack exchange，提问作者Tazmanian Tad