If you are referring to the button on the Windows 10 taskbar that showed a menu listing all files and folders on the Desktop, that was the Toolbars option on the Taskbar, that function is not supported on the Windows 11 taskbar, which has limited functionality compared to the Taskbar in Windows 10, also, the ability to move the Taskbar in Windows 11 is not available, it is locked to the bottom of the screen, there are some 3rd party utilities available online that claim to be able to move the Taskbar in Windows 11.
Microsoft are continuing to add new functionality to the taskbar in Windows 11, so the toolbars option like the Desktop may be added back, but they have indicated they do not intend to bring back the option to move the taskbar in Windows 11.