i have done that with no result (Mac mojave)
What Kirk showed should work (does for me…).
Have you enabled the check boxes
exactly as Kirk showed in the dialog? Also make sure you are actually searching a contact sheet that has files starting with the letter T…
Note that both the capital letter “T” and the lower case “t” will be matched. If you don't want that, check the box that says “Case Sensitive Search” (only “T” will then match).
Cheers,
Hayo