Добавьте файлы проекта.

zooManagerPro/Views/MainView.axaml.cs

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+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+using zooManagerPro.ViewModels;
+
+namespace zooManagerPro;
+
+public partial class MainView : NavigationPage
+{
+    public static MainView Current { get; private set; } = null!;
+
+    public MainView()
+    {
+        InitializeComponent();
+
+        Current = this;
+
+        Loaded += async (_, _) =>
+        {
+            await PushAsync(new LoginView()
+            {
+                DataContext = new LoginViewModel()
+            });
+        };
+    }
+
+    
+}