A spam attack on the pandoc-discuss mailing list hosted on Google Groups caused a suspension of the entire list. Google is not responding to request to re-enable the list.
For the time being, please use the GitHub Discussion feature. Whether this will become a permanent solution is currently not clear.
https://github.com/jgm/pandoc/discussions/

This also means that the archive with 15 years worth of mail has been lost, together with the knowledge that was available through those mails.
https://github.com/jgm/pandoc/issues/9250