This works for me:
my $folder = Vim::find_entity_view( view_type => 'Folder', filter => { 'name' => "Templates" } );
$folder->CreateFolder( name => "123");
You need to tell the method "CreateFolder" the new of the new folder as a hash.
Here you can find the docu: https://pubs.vmware.com/vi3/sdk/ReferenceGuide/vim.Folder.html#createFolder