[okanat]

I think they actually don't use that flag but use this function here: https://learn.microsoft.com/en-us/windows/desktop/api/Dwmapi...

The feature is from Windows Vista and it is still the basis of acyrilic effects on 11. The feature is explained in this page: https://learn.microsoft.com/en-us/windows/win32/dwm/customfr...