Not true at all. Here's one critical about Democrats as being too beholden to progressives: https://www.cnn.com/2021/06/11/opinions/democratic-party-pro...
Here’s one critical about the current Democratic VP largely for being too concerned with (and ultimately ineffective at) undercutting Republican talking points. https://www.cnn.com/2021/06/11/opinions/democratic-party-pro...
And that's just one day.
Except for stuff responding to new Trump-era revelations, they don't seem to have much current criticism of Republicans not buried within criticism of how Democrats deal with them, representing their actual bias in critical opinion coverage, in that it focuses on people currently in power.
(When Republicans held the White House and the Senate, they had more direct criticism of Republicans.)