There was a whole mini-industry around scraping specifically Reddit using the API feed because it was so open. AI companies first trained on Pushshift, which is like Common Crawl for Reddit, which is why Reddit shut down Pushshift (with legal threats IIRC) at the same time.

If there were a well-known URL that retrieved all content added to a site after a given date, and a meaningful number of sites implemented it, I bet the biggest scrapers would use it.

Except, of course, that then sites would start lying and sending abridged, poisoned, or nonexistent data.

Nice things cannot be had, no matter how many levels you go down.