- I'm thinking mostly about Internet-accessible media. That means social media, Internet-only news/opinion publishing, and legacy news/opinion media that underwent a transformation, from printing papers and running TV channels, to publishing articles on-line and running TV streaming. This is biased against media platforms that are still more focused on TV, radio and/or paper.
- I'm going by my own overall experience and exposure, which is likely biased by my interests and circles - STEM, software industry, higher education, and adjacent.
It feels to me that the "left/right" split in media is ~80/20, but I have no good way to estimate the the actual volume of right-leaning media, as I inhabit a left-leaning filter bubble[1]. That said, the reason I suspect there is some imbalance favoring "left" is because news publishing and advertising both focus mostly on-line these days, are run by well-educated people, and involve a lot of tech - and all those factors tend to lean left, AFAIK.
EDIT: also another factor suggesting an imbalance - there is clear one-sideness in terms of effective cancellation, performative victimhood and outrage activism - if there was no media bias, both extremes would be equally effective (or neither would be). This is not to say only one extreme is trying to manipulate people like this - I just suspect one side does it mostly through the media, and the other mostly through church sermons[2].
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[0] - The meaning of "right"/"left" I'm using here is the US one, as much as I internalized it. Over here in Europe, the "middle point" is located somewhere else, making the US "right" and "left" both be mostly on the same side - I just can't ever remember which one.
[1] - I don't seek out news myself, so I ingest mostly whatever happens to cross my way (and half of that is via HN anyway). My main exposure to more right-leaning media is through the government TV station my in-laws watch, and some talking point one of my parents picks up from weird and mostly partisan political YouTube channels.
[2] - The little exposure I had locally with Catholic sermons tells me that priests often push specific political / social views on the parishioners.