Typical cause: missing android:exported attribute in the main activity after targetting Android 12+. Add the attribute to your MainActivity.cs or manifest.

<activity android:name=".MainActivity"
          android:exported="true"
          android:label="@string/app_name">
</activity>

Rebuild and redeploy the app.

Ensure Info.plist has the correct UIRequiresFullScreen key set to true if using splash screen or custom renderers.

<key>UIRequiresFullScreen</key>
<true/>

Also verify the launch storyboard is correctly referenced.

Cause: Event handlers not unsubscribed. Use WeakReference or dispose pattern.

public class MyPage : ContentPage
{
    private readonly Button _button;
    public MyPage()
    {
        _button = new Button();
        _button.Clicked += OnClicked;
    }
    protected override void OnDisappearing()
    {
        base.OnDisappearing();
        _button.Clicked -= OnClicked; // Unsubscribe
    }
    private void OnClicked(object sender, EventArgs e) { … }
}

Ensure x:Class matches the code-behind namespace and class name. Clean and rebuild the solution.

<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MyApp.Views.MainPage">
    …
</ContentPage>