Hello,
Sorry to hear you are having issues. I think it can be done, you just need to create png file that is long and wide enough for your entire taskbar. For example if your taskbar is at size 1920x80 pixel, you will need to create a png file that big. But, once you apply that file, you can not resize your taskbar, I believe, Start11 do not have engine to stretch/compress your graphics like Windowblinds does. Dual monitor with different taskbar size will also not work.

Thanks
Basj,
Stardock Community Assistant.

Here a screenshot of taskbar.

Try this on your system.

Thank you,

Basj,
Stardock Community Assistant

I just realiced the Problem, brother, you helped me a lot. - It was simple! I was running my Resolution on 1080P, cause the taskbar was 1920. Was thought it fit. But i need to get 4K for windows. If not, it dosent work. 

You need to halfize it for 1080P, i learn.