Application notification manager throws on a partial trust application

[TheVeryStarlk]

Describe the bug

The AppNotificationManager fails to work on a partial trust application WinUI 3 project despite AppNotificationManager.IsSupported returning true.

Calling AppNotificationManager.Register throws System.Runtime.InteropServices.COMException: 'Unspecified error No COM servers are registered for this app'.

Calling AppNotificationManager.Show throws System.Runtime.InteropServices.COMException: 'The request is not supported. The request is not supported.'.

Steps to reproduce the bug

1. Create a MSIX packaged WinUI 3 project.
2. Change EntryPoint's value to windows.partialTrustApplication.
3. Comment out the runFullTrust & systemAIModels capabilites.
4. Call AppNotificationManager.Register (In OnLaunched before window activation) and/or AppNotificationManager.Show.
5. Observe the imminent existence of an exception.

Expected behavior

A regular Windows notification showing up.

Screenshots

No response

NuGet package version

2.1.3

Packaging type

Packaged (MSIX)

Windows version

Windows 11 version 23H2 (22631, June 2025 Update)

IDE

Visual Studio 2022

Additional context

No response

[hoshiizumiya]

#6479

[mominshaikhdev]

another manifestation of the root issue #219 which was closed without any path forward, the win32-app-isolation repo seems to be dead. I believe every partial trust or AppContainer issues require underlying OS changes.