csom-folder

using (var ctx = new ClientContext("https://intranet.demo.com/sites/test"))
            {
                var web = ctx.Web;
                var list = web.Lists.GetByTitle("Documents");
                ListItemCreationInformation lici = new ListItemCreationInformation
                {
                    UnderlyingObjectType = FileSystemObjectType.Folder,
                    LeafName = "TEST-CSOM"
                };
                var item = list.AddItem(lici);
                item.Update();
                web.Context.Load(item);
                web.Context.ExecuteQuery();
            }