Thank you for the suggestions. I tried them all except the last (I do not want to reset my File Explorer customizations), but the problem remains. Also, some of the steps outlined do not match my Windows version:
Clear the File Explorer history: Open File Explorer, click on the "View" tab in the ribbon, and then click on "Options." In the "Folder Options" window, click on the "Clear" button next to "Clear File Explorer history." This will clear the search history and may enable it to start working again.
This is incorrect. "Options" is available under the three dots on the Explorer ribbon, not under "View."
Check the Search settings: Open the Settings app by pressing the Windows key + I, then click on "Search" and select "Searching Windows." Make sure that the option "Search history on this device" is enabled.
This is incorrect. There is no "Search" option here. Where is it?