Seems to me that this is more of a monopolistic practice by Apple to be able to extract $26 billion for a default setting.
The problem with this whole mess is that monopoly, monopolization, and monopolistic practices were not defined by legislation. Legislation in fact provides no definitions whatsoever. The entirety of Section 2 of the Sherman Antitrust Act is comprised of a single run on sentence.
It's all well and good to be all "it's Mabo, it's justice, it's the vibe" over this, but congress hasn't provided legislation required to regulate competitive markets.
So the answer to your question is: monopolization is illegal according to the the Sherman Act, and the power to regulate markets is well within the (extremely broad) scope of existing laws (including the Federal Trade Commission Act and the Clayton Act).
https://www.ftc.gov/advice-guidance/competition-guidance/gui...