macOS - Navigation structure sidebar view vs full width / single column view

I'd like some help to structure navigation so that I can have an app that:
  • shows a sidebar view with a default detail view when it opens

  • clicking on each sidebar item loads the details view

  • clicking on an item in the details views pushes a full width view (without sidebar visible)

I just don't get how to use NavigationView to achieve this and none of the tutorials I've seen does something similar.

I've been stuck for quite a while on this and some guidance would save my week!

Thanks.
macOS - Navigation structure sidebar view vs full width / single column view
 
 
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