[Dwedit]

The start button is still a window, but it's not a top-level window. It's a child window of the taskbar. And has been so since Windows 95.

[ankurdhama]

Not anymore. On Windows 11 you can use spy++ to check the taskbar window and it will show up a single window and everything inside it, start button or program buttons, all are not a window. This seems to be the case for any app that is using <whatever is the new windows app framework>.