Thanks to Kit Baum, markstat 2.6 is now available on SSC. To update type -ado update markstat, update-

This release fixes a breaking change in Pandoc version 2.11, which uses --citeproc instead of --filter pandoc-citeproc to process bibliographies. If you want to use a bibliography you must update markstat and make sure you have installed Pandoc 2.11 or higher. Hat tip to Sam Harper for alerting me to this issue, which also bit Philip Miller.

The update also moves the injected CSS in HTML output files so it appears after the styles in the default Pandoc template. This allows users to override any style by creating a custom markstat.css file. Hat tip to Sam Stewart for this suggestion.