We rebuild the search index every fifteen minutes, so if you add new files or import files, they may not show up in file search results immediately. We do this to provide the fastest possible search experience, which we can only do by caching the search index. Providing real-time search could overwhelm our database due to the large number of new files added constantly.
However, you can see a list of the most recently added files using the "Newest Files" smart list from the "Filter by" dropdown in the file manager.