Old SkinStudio issues to remember while you are working on version 11
The problem with being unable to select specific target OS in SkinStudio advanced settings is still present in latest beta:: https://forums.stardock.com/492832/page/1/#3736944
I have not had time to test if 64bit Plugin DLLs for Titlebar buttons has been made available, need to find where I saved my copy of the SDK and my code from last attempt. But the thread has not been updated since you said "Please keep an eye on this thread for any updates. We appreciate your feedback and patience." almost 4 years ago: https://forums.stardock.com/493095/page/1/#3738609. And I do not know if the SDK is even downloadable anywhere at this time.