AvaloniaProjectApp/AvaloniaApplication2/Program.cs

using Avalonia;
using System;

namespace AvaloniaApplication2
{
    internal sealed class Program
    {

        [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();
    }
}