This is a purposeful alteration rather than a defect. Since the HTML export wizard for Impress and Draw was eliminated, LibreOffice 24.8.x is functioning as it should.
What’s left is a very simple HTML export that mimics the command-line impress_html_Export: everything is included in a single HTML page, with little structure, largely text, no slide navigation, and no separated assets. The previous presentation-style HTML that many remember from 7.x is essentially a legacy fallback.
For compatibility and scripting purposes, HTML is still shown in the export dialog. The filter remains, but without the wizard and the “slide show as a website” feature, as removing it completely would disrupt current workflows and CLI conversions.
Additionally, the more recent documents advise you to use SVG instead. If you want a slide that is both visually authentic and web-friendly, SVG is currently the suggested option. Instead of preserving the outdated Impress HTML pipeline, the initiative is obviously pushing users into other solutions if they want interactive online presentations.
Thus, the remaining HTML export is purposefully sparse, the documents lagged a little, and they were deprecated and eliminated on purpose. Despite the poor UX, it at least clarifies the discrepancy.