The transition of the classic Esri Story Maps templates to the later phases of the Esri Product Lifecycle was announced in 2019, and an update was shared in August 2021.
The classic storytelling templates went into extended support in September 2021. As a result of this transition, the classic Esri Story Maps website, which includes information and resources for working with Esri's classic storytelling templates, will no longer be maintained.
In a few months, we will begin the retirement of the classic website. An exact date has not been set, but this will not happen earlier than March 2022.
https://storymaps-classic.arcgis.com/
All customers are encouraged to use ArcGIS StoryMaps for new storytelling projects.
A resources page is available with tutorials, articles, and examples to learn more about telling stories with ArcGIS StoryMaps. A new community gallery was launched in December 2021 with many amazing stories created with ArcGIS StoryMaps that you can use to get ideas and inspiration for your own storytelling projects.
For more information about the status of the classic templates, see Classic story map transition timeline (August 2021) and FAQ: Classic Esri Story Maps and the ArcGIS Online... - Esri Community.