i used a sift search on windows office it was very quick searching all files to locate the file i wanted to open. as i typed into the search field each letter it would go and locate as you typed each letter in (eg)when you typed g it jumped to “g” file then type “o” it jumped to “GO” files and so on
You can change to use the OS open files dialog:
Menu/Tools/Options/LibreOffice/General - Open/Save dialogs.