Version

Windows 11 24H2(OS Build:26100.4351)
Win32 App Isolation Environment: MSIX-packaged WinUI3 app with AppContainer manifest

Repro Steps

Create a WinUI 3 MSIX-packaged app with appContainer set in the manifest.
The app acts as a COM client, attempting to use CoCreateInstance() to connect to a registered full-trust COM server.
COM server is properly registered (via manifest) and verified working when called from a non-AppContainer process.

Client calls CoCreateInstance( clsidIPCServer, nullptr, CLSCTX_LOCAL_SERVER, IID_IDispatch, (void**)&pDispatch);

https://1drv.ms/u/c/eadfcaf01eb3b9c8/ETBOJt42nLpKmLG-cgujSW0BtMkz3ATYKk0T-BD1WrqLhQ?e=m51Wer

Unexpected Results

CoCreateInstance() returns a failure HRESULT
No COM activation occurs; logs indicate security restriction
Server works correctly if launched from non-sandboxed Win32 app.
COM registration is valid and verified.