Question

that’s what i try but it return only the newest file from only the top directories under the root

if(Directory.Exists("YourPath"))
foreach (string _tempFiles in Directory.GetDirectories("YourPath")
                       .Select(directory => Directory.GetFiles(directory, "*.*", SearchOption.AllDirectories)
                       .OrderByDescending(File.GetLastWriteTime)
                       .FirstOrDefault()))

Answer 1

This returns all newest files of each directory(including root):

var rootDirFile = Directory
    .EnumerateFiles(yourPath, "*.*", SearchOption.TopDirectoryOnly)
    .OrderByDescending(f => File.GetLastWriteTime(f))
    .Take(1);
var allNewestFilesOfEachFolder = Directory
    .EnumerateDirectories(yourParth, "*.*", SearchOption.AllDirectories)
    .Select(d => Directory.EnumerateFiles(d, "*.*")
        .OrderByDescending(f => File.GetLastWriteTime(f))
        .FirstOrDefault());
// put both together, the root-file first
allNewestFilesOfEachFolder = rootDirFile.Concat(allNewestFilesOfEachFolder);

If there’s no file in a directory the file is null, so the number of files is equal to the number of folders.

Note that Linq is not the right tool for System.IO since error-handling is difficult.