Hello,
Please note that the current stable version of phppptx supports a set of contents and styles detailed on addHtml (https://www.phppptx.com/documentation/api-documentation/contents/add-html-pptx).
Your HTML includes unsupported tags and styles, such as images or slides. In these cases, you need to call PHP API methods, such as addSlide (https://www.phppptx.com/documentation/api-documentation/contents/add-slide-pptx) to add slides.
New releases of phppptx add support for new tags and styles when transforming HTML to PPTX. We are also developing HTML Extended and CSS Extended to be included in phppptx Premium licenses, which will support calling phppptx methods from HTML tags. It's a work-in-progress task that will be added in a future release of phppptx.
Regards.