If the Auto-Hide Taskbar feature is not working in Windows 11, then here are some suggestions to help you resolve the issue successfully.

On the right side, scroll down and click on Taskbar. Choose Taskbar behaviors. Uncheck the Show hover cards for inactive and pinned taskbar apps option to disable the hover cards.

Auto Hide Desktop Icons is a free app that can hide your Windows desktop icons and even your taskbar, automatically after a set time interval.