If your ebook is epub3, to enable embedded fonts for iBooks, you will need to add <meta property="ibooks:specified-fonts">true</meta> in the metadata section of the content.opf file. The com.apple.ibooks.display-options.xml file is not needed.
Code:
<?xml version="1.0" encoding="utf-8"?>
<package version="3.0" unique-identifier="BookId" xmlns="http://www.idpf.org/2007/opf">
<metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
<dc:identifier id="BookId">urn:uuid:c6753a11-b049-4b2d-99e5-445b301adab5</dc:identifier>
<dc:language>en</dc:language>
<dc:title>[Main title here]</dc:title>
<meta property="dcterms:modified">2021-04-27T08:47:09Z</meta>
<meta property="ibooks:specified-fonts">true</meta>
</metadata>
<manifest>
<item id="Section0001.xhtml" href="Text/Section0001.xhtml" media-type="application/xhtml+xml"/>
<item id="sgc-nav.css" href="Styles/sgc-nav.css" media-type="text/css"/>
<item id="nav.xhtml" href="Text/nav.xhtml" media-type="application/xhtml+xml" properties="nav"/>
</manifest>
<spine>
<itemref idref="Section0001.xhtml"/>
<itemref idref="nav.xhtml" linear="no"/>
</spine>
</package>
You can check the
Apple Books Asset Guide 5.2.12 for more information (or a cure for insomnia
).