Apple owns the App Store but does not own the iOS apps (other than Safari, Keynote, Numbers, Pages, GarageBand, etc.) nor do they own the alternative app stores like AltStore PAL, Mobivention Marketplace, Setapp Mobile, etc. The alternative iOS app store/distribution market is what was created once Apple stopped unfairly blocking (at least in the EU so far) that market from being able to exist.
It was anticompetitive in the EU which is why alternative iOS app stores are now being allowed. Potential rulings/decisions in other countries are still up in the air.