You can’t add a beforeInsert datahook to any collection in either of the Wix Blog or Wix Forum apps.
You can see this yourself if you go to your site structure and click on the cog settings icon for any of the Wix Blog or Wix Forum collections and go through the add a datahook section.
You can only add badges as per the Wix API Reference.
https://www.wix.com/corvid/reference/wix-users-backend.badges.html