Apple is the smaller company in a duopoly market. There are not enough players in the market that dissatisfied customers can easily up and leave.
The real harm we see Apple doing is that they allow the dominant groups in society to suppress anyone else. This became especially clear during the Hong Kong protests, where they banned apps protestors used after a request from Chinese authorities. Because of the lack of choice in the market, consumers have little choice but to live with whatever is imposed on them.
When you consider "monopoly" or "market unfairness" you have to look at it on the state level. I don't think anyone is complaining about Europe where Apple is in the minority of phones. I would assume we're talking about the USA where Apple does have outsized influence compared to other phone brands. We aren't talking about Apple vs Google. It's Apple vs Samsung/Google Pixel Line/Motorola/Nokia and their abuse of their status as the largest phone seller in the USA. Say iMessage policy being limited to the Apple platform as others have pointed out.
The real harm we see Apple doing is that they allow the dominant groups in society to suppress anyone else. This became especially clear during the Hong Kong protests, where they banned apps protestors used after a request from Chinese authorities. Because of the lack of choice in the market, consumers have little choice but to live with whatever is imposed on them.