I don’t have a link right now, but if you look it up at the usual suspects like wired, ars technica, the register, 404 media, or even Ed Zitron or Cory Doctorow, I’m sure you’ll find plenty of stuff. The search degradation started around the time Sundar Pichai became CEO at Google and it made quite a splash during all that time. Also, there have been several “rollouts” in recent years which changed the search result appearance, content and the page rank algorithm over time, this was published by Google itself. They did of course not disclose how the algorithm works.