It seems the search bar in the Media Library is scoped to the WP Media Folder folder selected at the time of the search. This is usually really helpful to limit the results and quickly find what you're looking for. However, there are times when you might not know which folder a file is in. It would be great to have the option of selecting the top-level Media Library "folder" and allow a library-wide search in all the folders to be returned.
This would save a lot of time not having to search every main folder for the same file to see if it's somewhere in the library.
Thanks for considering this enhancement request