What makes the taskbar hide exactly when I need to click it?

Start by turning off auto-hide: right-click an empty part of the taskbar → Taskbar settings → Taskbar behaviors → untick “Automatically hide the taskbar.” It should then stay visible during normal desktop use.

If that option is already off, or the taskbar still disappears, press Ctrl + Shift + Esc to open Task Manager. Find Windows Explorer under Processes, right-click it, and choose Restart. The desktop and taskbar will briefly disappear while they reload.

Also notice whether it happens only with one app open. Full-screen games and videos can cover the taskbar even with auto-hide disabled. For a browser, press F11 to leave full-screen mode and check again.

If you use a taskbar customization tool, temporarily disable it too—it may be controlling the hiding behavior separately from Windows.