isn't this crawler to generate previews on Facebook? they have others for training and AI stuff. oh well, one never knows with Meta...

—— The facebookexternalhit/1.1 user agent you're seeing in the logs is a Facebook crawler, specifically used by Facebook’s servers to fetch content (like Open Graph metadata) when:

Someone shares a link on Facebook or Messenger

Facebook needs to generate a preview (title, image, description) for that URL