And dozens of essays by post-modern philosophers about (e.g. Public Opinion Does Not Exist by Bourdieu [1972]) and subsequent psychological studies about inherent biases, which together pretty resoundingly proves the non-existence of unbiased media. Furthermore it shows that biases correlate with benefactors, so you can expect more biases in platforms which rely on shareholders, named donations or advertisements.

I don't know about a movie, but there have been several books written about media bias by people in the media. One example is Bernard Goldberg's book "Bias." (https://www.amazon.com/Bias-Insider-Exposes-Media-Distort/dp...)

It's an age old trope - just look at the Daily Bugle.