Being left-leaning is not cause for antitrust. Making your argument a false equivocation. Should Google be subject to antitrust trials? I would say yes, but not because of a left or right leaning bias in their search results.
There isn’t any credible alternative to Google because they’re head and shoulders above everyone else.
There are other search engines, they just don’t measure up.
But I actually think you raise an extremely interesting question: does pushing a political agenda using your monopoly position constitute an abuse of monopoly power?
The advent of privately controlled monopolistic forums is somewhat new. I don't think it's at all obvious how the spirit of anti-trust law should be extended in the age of platforms...
We're in new territory.
As horrible as this may sound, it is a cause for anti trust break up when those in power are right leaning.
I mean, let's not split hairs here. As a matter of pragmatic reality, that's pretty much what it comes down to.