I recently revisited Apple Books and noticed it has undergone significant changes. The new customization options for margins, spacing, and text justification have greatly improved the rendering of my epub files. However, there is a minor and longstanding issue: the cover does not display correctly unless edited with Calibre using "mark certain image as cover image." After checking the differences between the old and new epub files post-saving, I found out that only one line requires modification.
Locate the metadata section within the content.opf file, identify the tag <meta name="cover">, and update its content to match the id of the image item listed in the subsequent manifest section. For example, the content of the meta tag named "cover" should be updated to "img_html_images_cover".
Code:
<meta name="cover" content="Images/html/images/cover.jpg"/>
...
<item id="img_html_images_cover" href="Images/html/images/cover.jpg" media-type="image/jpeg" />