I recently built this for a client:
https://github.com/paviliondev/discourse-pm-topic-author
It is open-source. It may suit your needs. Just add the Categories you want it to appear in. Let me know if you hit any bugs.
Unfortunately I don’t have time to extend it at present.
Thanks to @davidkingham for commissioning us to do the work and allowing this to be open source, and in turn therefore supporting the wider community.