Microsoft has added a ‘Start_ShowClassic Mode’ registry key that allows you to revert back to the classic Windows 10 Start Menu. The new Windows 11 Start Menu is taken from the now-shelved Windows 10X and has significant differences from the Classic Start Menu, including a floating pane and a redesigned layout. To enable the classic Start Menu in Windows 11, you can either download a Registry file that can enable the feature for you or modify the Windows Registry to enable it. The easiest method is to simply download the show-classic-start-menu.reg Registry file and save it to your desktop.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-11-lets-you-enable-the-classic-windows-10-start-menu-heres-how/