What actually don't work? Please elaborate. Perhaps add more screenshot with pointer, pointing to the "not working" area or a short video grab.
End of basj's quote
Anything more on this one.
Below is my screenshot on Start11 v2.72 on Windows 10. The rounded corner does work on Windows 10.

Looking on your screenshot, I have few questions.
- What application use to make Windows title bar transparent?
- Your second screenshot showing partial Start menu with bottom Taskbar, that one have rounded corner taskbar, but your Start menu look different, which Start11 start menu style was that one on? Or is there another 3rd party software was use?
Thank you,
Basj,
Stardock Community Assistant