AvaloniaProjectApp/AvaloniaApplication2/App.axaml.cs

using Avalonia;
using Avalonia.Controls.ApplicationLifetimes;
using Microsoft.EntityFrameworkCore;
using Avalonia.Markup.Xaml;
using AvaloniaApplication2.Models;
using AvaloniaApplication2.ViewModels;
using AvaloniaApplication2.Views;
using Microsoft.Extensions.DependencyInjection;
using Avalonia.Data.Core.Plugins;

namespace AvaloniaApplication2;

public partial class App : Application
{

    public override void Initialize()
    {
        AvaloniaXamlLoader.Load(this);
    }

    public override void OnFrameworkInitializationCompleted()
    {
        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
        {
            //Îòêðûâàåì îêíî àâòîðèçàöèè ïðè çàïóñêå ïðèëîæåíèÿ
            BindingPlugins.DataValidators.RemoveAt(0);
            desktop.MainWindow = new MainWindow
            {
                DataContext = new MainWindowViewModel(),
            };

        }
        base.OnFrameworkInitializationCompleted();
    }    
}