Yes. clarkwinkelmann is right about it. I just changed the permission, then all visitors can search user.
@IanM after I click "Filter by author" then the cursor won't automatically goes to the input box, on the other hand, the text below the input box, says "start typing", yet the text I type won't appear in the input box.
Excuse me for raising such a picky issue. 😅 Thanks very much for working on this extension. 😄