Vizual_Zurnal/Zurnal_Vizual/App.axaml.cs

using System.Linq;
using Avalonia;
using Avalonia.Controls.ApplicationLifetimes;
using Avalonia.Data.Core.Plugins;
using Avalonia.Markup.Xaml;
using Zurnal_Vizual.Views.MainWindow;

namespace Zurnal_Vizual
{
    public partial class App : Application
    {
        public override void Initialize()
        {
            AvaloniaXamlLoader.Load(this);
        }

        public override void OnFrameworkInitializationCompleted()
        {
            if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
            {
                DisableAvaloniaDataAnnotationValidation();

                var mainWindow = new MainWindow
                {
                    DataContext = new MainViewModel(), 
                };

                desktop.MainWindow = mainWindow; 
            }

            base.OnFrameworkInitializationCompleted();
        }

        private void DisableAvaloniaDataAnnotationValidation()
        {
            // Get an array of plugins to remove
            var dataValidationPluginsToRemove =
                BindingPlugins.DataValidators.OfType<DataAnnotationsValidationPlugin>().ToArray();

            // remove each entry found
            foreach (var plugin in dataValidationPluginsToRemove)
            {
                BindingPlugins.DataValidators.Remove(plugin);
            }
        }
    }
}