For videos it can’t find metadata for, Jellyfin will either display only the title (if you set the library type to “movies”), or it will extract a random frame

For videos it can’t find metadata for, Jellyfin will either display only the title (if you set the library type to “movies”), or it will extract a random frame from within the video to use as the image (if you set the library type to “home videos”). In both cases, the video isn’t going to be hidden.