"Apple does not allow apps to be installed on iOS devices outside of the App Store and there are no alternate app store options that are available."
Not exactly. Businesses can deploy internally-developed apps to their employees, if they have an Apple Developer Enterprise Program membership.
That still have to be reviewed by Apple and can be rejected. Still have to have permissions. The only difference is that those apps don't appear in the general app store and appear in something like Intune that also has to have Apple approval and review.