If you mean Apple owns and runs an App Store, then yes, but that’s not a monopoly. It’s just a store that they control. Would you say that their physical stores are a monopoly that they abuse by not selling samsung phones?
Regardless, their behaviour with their own Dev relations is very much like what they're accusing Qualcomm of.
That’s not a monopoly. That’s them exercising control over their own property.
What’s the rationale to treat Apple’s digital store different than Apple’s physical store?
They also refuse to permit their customers to run apps not approved by Apple on the phones they have bought. That's the monopoly.
and they still sign your apps, they just do it automatically, i think.