It’s not global percentage of a certain market that defines a monopoly.
Apple has 100% market share in the iOS market. Due to that fact they’ve got exclusive control over a significant percentage of the population - consider that customers cannot install another OS on the hardware they’ve bought and they cannot move their iOS apps on another Android phone either.
To make an analogy consider that you’d complain about your local electricity provider having a monopoly and I’d tell you that you can always move to another city or country, there, problem solved, it was your fault for staying there.