Application Descriptor - Full Stack

Hi Experts,

I am trying to edit my manifest.json in App. descriptor in Full stack. I choose Neo free trial as I am practicing some examples.

I am not seeing the option to edit the file in descriptor mode. I choose this option as default editor and have choosen the project settings as "SAP Fiori". I am still not getting this option. Am I missing something or is this a bug in Full -stack. Thanks