First, the software giant is changing the look of the Start Menu. This is a change that's been documented before, the new Start Menu will have a more uniform look:
We are freshening up the Start menu with a more streamlined design that removes the solid color backplates behind the logos in the apps list and applies a uniform, partially transparent background to the tiles. This design creates a beautiful stage for your apps, especially the Fluent Design icons for Office and Microsoft Edge, as well as the redesigned icons for built-in apps like Calculator, Mail, and Calendar that we started rolling out earlier this year.
Next, Microsoft is changing the default behavior of the Alt-Tab feature. If you use the Edge browser, all tabs open in Edge will start appearing in Alt + Tab. Microsoft is testing this feature on a subset of Insiders today. Users will still be able to switch back to the old Alt+Tab behavior via Settings > System > Multitasking.
There are also some updates for the taskbar, a new notification experience, some changes to the Settings menu, and improved tablet experience for 2-in-1 devices. Also good to know is that Microsoft is rolling out Windows Calculator graphing mode feature to the public.