At the moment the ZIM generation is finished, you get a "Rendering finished" Web page.
This page provides a link to the generated ZIM file:
The document file has been generated. Download the file to your computer.
IMO, a browser download dialog windows should also automatically popup. So the user should not be forced to click manually on the link to get the ZIM file.
Version: unspecified
Severity: enhancement
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=42991