When I press Ctrl + F to search in File Explorer, the search box does not receive focus.

Hey — Ctrl+F should normally move focus to File Explorer’s search box, so the fact that restarting Explorer fixes it points to Explorer losing its keyboard-focus state.

First check whether Ctrl+E gives the same result; it is another shortcut for the Explorer search field. If both fail, restart Windows Explorer from Task Manager and test with third-party Explorer add-ons, clipboard tools, and keyboard/macro utilities disabled. A clean boot is a good way to find a program stealing the shortcut.

If the issue also appears in a fresh Windows account, run `DISM /Online /Cleanup-Image /RestoreHealth` followed by `sfc /scannow`, and install the latest supported cumulative update. Please share your `winver` build and whether Ctrl+F still works in browsers and Notepad.