The overhauled UI includes a redesigned Start menu, new system icons, rounded corners and redesigned hubs for Action Center and Settings, plus revamped core apps like Painter, Notepad etc. The store side is rumored to offer more incentives for developers, and the support for big.LITTLE cores will bring changes to the CPU scheduler.
https://www.notebookcheck.net/Windows-11-rumored-to-launch-this-October-with-overhauled-UI-improved-Microsoft-Store-and-support-for-Intel-Alder-Lake-big-LITTLE-cores.544054.0.html