Given that Apple always restricts access to their tech to Apple products and limits them in some way that enforces that restriction, and given that Apple has 17% of the desktop/laptop market and 20% of the phone market, while it would be sort of a monopoly for Apple products (which by that logic means macOS and iOS constitutes a "monopoly" as well) it's really hard to see how it would be a monopoly in any sense that word is used in any legal sense.
And it would hardly prevent users from installing other AI apps, they just wouldn't be as integrated.
Musk is, as always, a whiny idiot.