WPD2HTML does not create any HTML elements or styling to properly display vertical text columns from WP6 (2021) files. Regardless of column style type, only paragraph elements with spans containing the text content are created. libwpd recognizes the column style groups in the WPD and does SOME handling of them. However, it doesn't use RVNGHTMLTextGenerator to build a table or create styling to render the elements it creates side-by-side with a gap in the middle. Instead the paragraph and span elements are just created normally and appear as new lines.
Have you tried adjusting any settings or configurations within WPD2HTML to see if that resolves the problem? https://tunnelrushgame.io