There's approximately 2 app stores, I wouldn't call that competition.
Even in the most egregious days of Microsoft's OS monopoly, you could still choose to install software. Apple makes it basically impossible to do this outside of the context of their app store, which they charge heavily for access to and have no qualms removing or preventing apps that compete with its own. If this doesn't constitute monopolistic behavior, the bar is so high I'm not sure anything would ever qualify for it.
Even in the most egregious days of Microsoft's OS monopoly, you could still choose to install software. Apple makes it basically impossible to do this outside of the context of their app store, which they charge heavily for access to and have no qualms removing or preventing apps that compete with its own. If this doesn't constitute monopolistic behavior, the bar is so high I'm not sure anything would ever qualify for it.