Update Document Properties using C# - SharePoint Online

Question

I have a drop off library in a site collection on a SharePoint Online tenant and I am writing a C# console application to update properties of uploaded documents, my code doesn't seem to update the properties, can someone tell me what I am doing wrong or missing?

Please note, this is SharePoint Online tenant.

using (var context = new ClientContext(webUrl))
        {
            context.Credentials = new SharePointOnlineCredentials(cm.Username, password);
            var web = context.Web;

            // Get drop off library and edit all items without making changes
            context.Load(web, w => w.Lists);
            context.ExecuteQuery();

            List dropOffLibrary = web.Lists.GetByTitle("Drop Off Library");
            context.Load(dropOffLibrary, dl => dl.RootFolder.Files);
            context.ExecuteQuery();

            foreach (var file in dropOffLibrary.RootFolder.Files)
            {
                context.Load(file.ListItemAllFields);
                context.ExecuteQuery();
                file.CheckOut();
                context.ExecuteQuery();
                var title = file.ListItemAllFields.FieldValues["Title"].ToString();
                file.ListItemAllFields.FieldValues["Title"] = title + "1";
                file.Update();
                context.Load(file);
                context.ExecuteQuery();
                file.CheckIn(string.Empty, CheckinType.OverwriteCheckIn);
                context.ExecuteQuery();
            }

            context.Load(dropOffLibrary, dl => dl.RootFolder.Files);
            context.ExecuteQuery();

            Console.WriteLine("Paused... (end)");
            Console.ReadLine();
        }
    }

Answer 1

Try Following code

            foreach (var file in dropOffLibrary.RootFolder.Files)
            {
                context.Load(file, f => f.ListItemAllFields);
                context.ExecuteQuery();
                var title = file.ListItemAllFields.FieldValues["Title"].ToString();
                ListItem newItem = file.ListItemAllFields;
                newItem["Title"] = title + "1";
                newItem.Update();
                file.Update();
                context.Load(file);
                context.ExecuteQuery();
            }