WindowsTaskbar.setThumbnailToolbar not working

[Hexagon95]

If I run the example from here, it's working and It's perfectly fine.
But If I make a new project and copy everithing, and follow all instructions, this feature WindowsTaskbar.setThumbnailToolbar will not work. (the rest of the features are still fine). I use Windows 10.
I did include all assets in pubspec.yaml, is there a property somewhere, where I should set something to "enable" ?
like AndroidManifest.xml in Android? :)

thank you in advance for your feedback.

[alexmercerind]

Do you see some exception being thrown? Any details will help me in saying anything.

[Hexagon95]

:( But if I clone the whole git repository, then it will work. So I don't see what I do wrong. :(