Fox News is not mainstream media.

Fox News was the top news outlet for 5 years in a row as of 2020. How is that not mainstream??

Fox News is right-wing propaganda, explicitly set up to steer the country into the fascism that is currently eating the Constitution.

What part of that precludes it from being mainstream?

I hate to be the one to tell you, but the right wing propaganda machine setup to prevent another Watergate scandal worked better than the creators ever could have expected.