My father had this issue, could not click on the search box, and it resolved when I changed the display options for the desktop and colors for windows/file explorer, and has not recurred. Changed default
windows mode to dark, default app mode to light, and set a custom accent color. Don't understand how they could be related, but the search started working again and it stayed fixed after a reboot.
I did this from settings, personalization, colors, but I don't see how you can change default app mode settings, or the specific colors for explorer. It's probably something simple I'm missing. How did you do that?