In c# we can easily get a file thumbnail of any file (not just images) using shell.
One of the ways I have been doing it in my desktop software is
HResult result1 = ((IShellItemImageFactory)ppsi).GetImage(new SIZE(resolution, resolution), SIIGBF.SIIGBF_BIGGERSIZEOK | SIIGBF.SIIGBF_THUMBNAILONLY, out hbitmap);
or for icons
var shInfo = Shell32.GetFileIcon(path, Shell32.FileAttributes.Icon);
Unity does not report any errors but just crashes the editor once it reaches those lines.
Is that even possible in Unity? I do plan to target only desktop computers.