The user config is now implemented per @kris.kotlarek
https://github.com/discourse/discourse/commit/243efa89318d0de1b67aba9087c58c252a1d540a
There is a site setting to control the default, but it is hidden form now, to change the default:
On our hosting: contact teams support
On self hosting: SiteSetting.default_sidebar_list_destination = 'unread_new' in a console.