Selecting story thumbnails
To specify story thumbnails, hovering over the thumbnail area at the top of the Main properties tab on the right:
Then, select Pick a thumbnail:
Search for a Photo to assign as the story thumbnail or upload it by selecting the Upload button:
In the case of a story with many translations, when selecting the thumbnail, editors can apply it to all translations:
Note: If you choose the option Set as thumbnail for all translations, the selected image applies as a thumbnail to all the languages you have permission to operate on.
Once set, the thumbnail displays in the story editor page: