Your first link supports your claim, the second is literally the WSJ reporting it. I do believe Biden’s closest circle worked to cover it up but I don’t think there was a coordinated effort by the media.
The second link is CNN attacking the WSJ article about the article they wrote. Here is Joe Scarborough attacking claims about Biden declining: The Guardian called it the most unreported story story: Joe Biden’s decline called most ‘under-covered’ story of 2024 The White House and Democrats went after anyone that even suggested Biden was declining with such fury that I think it caused a lot of newsrooms to realize that if they covered it, they would lose access with the White House and would be persona non grata with Democrats. Instead of making them more curious, they backed off and did not pursue the story, which allowed the White House and Democrats to set the narrative and there was no reporting to dispute it other than the WSJ and Alex Thompson, who were accused of reporting misinformation because no one else was reporting on it.