There's a relevant engineering axiom, that a sufficient quantitative difference amounts to a qualitative difference (sometimes phrased as "quantity has a quality all its own").
At some ineffable point, a "private platform" of sufficient scope becomes a Commons, resembling a social substrate more than a mere voluntary exchange between individuals. A historical equivalent would be "company towns", with goods only available from company stores, exchanged in company scrip, etc. [0]
Obviously, from a purely legal perspective, you are 100% correct. Google is under no obligation to uphold a principle of free speech, non-favoritism, etc., and it would take significant new legislation or regulation to change that.
Nonetheless, in terms of the role that is being played in society and culture, tech giants in general, and Google/Facebook in particular, are wielding disproportionate (and arguably ideologically biased) influence, bordering on an attempt to control narratives and ideas. It's perfectly legitimate to find this trend concerning without supporting the particular ideas being suppressed (I think Plandemic/InfoWars/etc, are utter nonsense).
I believe such actions tend to be counter-productive: (a) isolating and ostracizing those who are falling for bad ideas only reinforces their beliefs and persecution complex, while obstructing the path back to better ideas; and (b) every once in a while a seemingly-crazy idea turns out to be true (it's instructive the extent to which it was a fight uphill for germ theory to be accepted by the experts of the day [1]).
There simply isn't a magic wand that sifts good ideas from bad, a priori; and if the power to make that decision is centralized, even with the best of intentions, whoever wields it will inevitably make mistakes.
[0] https://en.wikipedia.org/wiki/Company_town
[1] https://en.wikipedia.org/wiki/Germ_theory_of_disease#John_Sn...