KFind is a standalone search tool from KDE. It has finer grained search than the default search in Dolphin (the file manager) and it just seems to be better at finding files.
To install KFind in KDE neon, open Konsole and type,
sudo apt install kfind
Enter your password and the program will install. After installation you can find KFind in the Applications Menu under Applications/Utilities or by searching for KFind at the top of the menu. You will also be able to open it from with Dolphin by selecting Find and then the More Search Tools menu on the right.