No, there isn't any question that some of the major media is biased to the left. Bias is prejudice in support of or against something. I would like to imagine you're capable of looking up words for yourself.
Yes, there is question about that. I know what the word means, the question is whether you do. And it's clear you don't know what the word means.
The only bias here is your bias, to make the false claim that some of the mainstream media shows a left-wing bias. That's a claim made for many decades by the right, repeated loudly and often enough to get some people to adopt it and parrot it, as you do.
Let's take as an example, the current impeachment issue.
There are a lot of statements the news media could make. They could call it a witch hunt (as I assume Fox has), they could call it solid investigating, they could say trump did nothing wrong, they could say trump organized an effort to withhold things Ukraine wanted to try to pressure their president to say what trump wanted, they could say it was an abuse of power, they could say trump threatened to nuke Ukraine.
That last would be an example of ACTUAL 'left-wing bias' - exaggerating the known story falsely, to make it worse on trump - there is no known case if it being said by mainstream media.
The rest - there are facts, there are opinions, there are positive and negative statements, but none of them, even if negative about trump or Republicans, is "bias" for that alone. It takes more to be "bias".
More that you have not shown. You provided no evidence of any widespread mainstream liberal "bias"; you provided not even one example.
What you did show is that you believe what you are told many times, in this case. There are a lot of difference political views, and as such, many people easily wrongly see some news as 'biased'. Even 'shaping' news coverage to a political audience doesn't mean "bias". Does covering more or less about issues liberals care about mean "bias", no matter how accurate and fair? To you, yes.