Choto/AvaloniaApplication3/MainWindow.axaml.cs

using Avalonia.Controls;

namespace AvaloniaApplication3;

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void OnRegistrButtonClick(object sender, Avalonia.Interactivity.RoutedEventArgs e)
    {
        var registratorWindow = new Registrator();
        registratorWindow.Show();
    }
}