Last week of November 2019, FOX average total audience was 3.015 million viewers.
https://www.forbes.com/sites/markjoyella/2019/11/26/fox-news-cruises-to-records-as-it-hits-215th-consecutive-monthly-ratings-victory-in-november/?sh=7eabbd8642b5
Fast forward a year, and Fox dropped quite a bit....
https://www.pacificpundit.com/2020/12/02/fox-news-ratings-continue-to-tank-still-below-msnbc-for-nov-30/
...with some shows not beating FOX since 2001.
Look at the numbers in the posts you linked:
Nov 2019 from the first link: average total prime time audience of 2,779,000
Nov 2020 from your second link: Fox News 2,645,667
That's barely a change, and not a collapse!