For help with https://github.com/davidortinau/WeatherTwentyOne please post in that github. The ToastContentBuilder is part of the Windows Community Toolkit from https://github.com/CommunityToolkit/WindowsCommunityToolkit
An error is here: .AddAppLogoOverride(new Uri("ms-appx:///Assets/dotnet_bot.png"))
The ms-appx: URI refers to assets in your app package and isn't meaningful in your unpackaged application.
You should be able to use a file URI instead of an ms-appx uri.
See the documentation for ToastContentBuilder.AddAppLogoOverride for details.