GsaViewer/GsaEditor/App.axaml.cs

using Avalonia;
using Avalonia.Controls.ApplicationLifetimes;
using Avalonia.Data.Core.Plugins;
using Avalonia.Markup.Xaml;
using GsaEditor.ViewModels;
using GsaEditor.Views;

namespace GsaEditor;

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

    public override void OnFrameworkInitializationCompleted()
    {
        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
        {
            // Avoid duplicate validations from both Avalonia and the CommunityToolkit.
            var dataValidationPluginsToRemove =
                BindingPlugins.DataValidators.OfType<DataAnnotationsValidationPlugin>().ToArray();
            foreach (var plugin in dataValidationPluginsToRemove)
                BindingPlugins.DataValidators.Remove(plugin);

            desktop.MainWindow = new MainWindow
            {
                DataContext = new MainWindowViewModel()
            };
        }

        base.OnFrameworkInitializationCompleted();
    }
}