Problem
The background is always transparent no matter what color is chosen in the widget's config.
Root cause
Android 11 introduced some changes about storage and its access.
The background is actually an image that I create based on your chosen color.
There now seems to be a problem writing/reading this image, therefore the background is transparent.
Solution
Currently none :(
The widget and its code are pretty old so I am having trouble recompiling it.
I hope I can fix it at some point in the future but I cannot make any promises.