Here's an article from 2014 discussing fake news: https://www.bostonglobe.com/arts/2014/08/30/large-the-intern...
Here's an article from 2011 discussing the measures taken against fake news (to little effect) since 2006: https://www.freepress.net/blog/11/12/21/truth-about-fake-new...
https://gizmodo.com/facebooks-fight-against-fake-news-was-un...
My memory is the same as the comment you are replying to. "Fake news" was a left attack on the media supporting Donald Trump (think Breitbart). Trump and friends then coopted the term to describe the mainstream media and repeated it enough for the term to become associated more as Trump-thing than anything else.
1 - https://trends.google.com/trends/explore?date=today%205-y&q=...
No, "fake news" was used to label news that was quite literally fake. As in: false. Not true. It was not used to describe simply biased reporting.
As others have said, Trump co-opted the term and uses it to describe news that he doesn't like, regardless of truth. Thus, he has muddied the meaning of the term and created a new dog whistle. Brilliant move on his part.
Fake news was generated to appeal to all sides of the political spectrum, but the pro-right literally untrue news was much more popular than the pro-left literally untrue news.
This is a good article on the subject: "Inside the Macedonian Fake-News Complex" https://www.wired.com/2017/02/veles-macedonia-fake-news/
It's opens:
"The first article about Donald Trump that Boris ever published described how, during a campaign rally in North Carolina, the candidate slapped a man in the audience for disagreeing with him. This never happened, of course."
No, it came into popular usage to refer to propaganda supporting Trump which closely followed what RAND Corp. labelled the “firehose of falsehoods” propaganda strategy used by Russia.
It was subsequently co-opted by Trump in the way you describe, but that's not how it came into popular usage.