How on earth is that a monopoly? It's their product. That's like saying MS have a monopoly on Windows. Or VW have a monopoly on the Golf.

There's literally nothing stopping anyone else from developing an AirTag competitor.

It's more like... Apple doesn't really have much reason to open up their technology here to third parties and it doesn't make sense to, either. It's not whether or not other people can design applications for something like a gigantic mesh network other than Apple, just that in order for such a thing to be useful it has to be opt out, which means that the application would have to be developed in conjunction with Apple or by Apple.

If you allow third party applications utilize the tech but require an opt-in, it's effectively useless. If you allow third party applications to do so without an opt-in, it's dangerous.

I think this particular usage of monopoly is suspect/leading.

Tile has a monopoly on Tile devices. Ford has a monopoly on F-150s.

Yes a company has a monopoly on its products in many/most cases. That doesn’t mean they have a monopoly on the market though.