This kind of thing reminds me of why I've always felt there shouldn't be a gatekeeper. Add your repos, install your apps. Folks should be allowed to have more than one repo to install apps from.
But if you allow users to have freedom, grandma will get hacked! We should all be told what to do and where to go and rely on gatekeepers for permission, for safety. (And no, of course there’s not any solution that would allow competent individuals to go outside the safe zone.)
In my opinion, the Apple app store should actually be FAR more curated than it is, and far less curated options should be equally available. The Apple App store (and the Google app store for that matter), should be a relatively small list of apps that have extremely high standards and guarantees. It should essentially be impossible for spammy bullshit to get into these places. User-controlled, parental control like options should determine whether or not other app sources can be installed from (including allowing for specific other sources, so that app source control can be granular and detailed. I should be allowed to add FDroid but nothing else for example).
Done. Problem solved. Everyone is happy. Grandma is safe and Johnny has control over his phone.
But of course, that assumes that keeping Granny safe is actually the reason. Facially obviously, it is not, and is in fact entirely pretextual.