Diarium version:
OSX 11.6 + Diarium 2.8.5
When selecting 'Export'
File format: "Web Page"
and check the 'Create separate files for attachements'
then clicking the 'Export' button,
The file that is output has a .html extension but it doesn't render in the browser. It turns out that it is a zip file. Renaming the file to end in .zip and extracting it works fine. But it wasn't obvious.
Also the web page that is created in the zip uses img tags with data:image embedding. It would be nice to reference the exported attachments so the html file size doesn't get so massive. (Let me know if you want a separate ticket for that)