Hello,
there is no DPI setting for HTML in the PDF24 Toolbox. Since version 11.31.0, PDF24 converts PDF to HTML with its own converter (Convert from PDF, format HTML, mode Complete). It takes over the images of the PDF as separate images in their original resolution, so they are not reduced to a fixed DPI. Only content that cannot be taken over as a separate image is drawn into a page background, which has a fixed resolution of 150 DPI.
If you are still using an older version, please update and try again. The conversion is also available online: https://tools.pdf24.org/en/pdf-to-html
Thank you for the suggestion of a DPI setting for HTML, we will add it to our list.