Earlier quoted context omitted.
Somehow this is not a problem on Android even though they have sideloading and alternative app stores even beyond what Apple is going to allow. (Apple still requires apps to go though a review process, even if distributed outside of the App Store, and will enforce this using digital signatures.)
This is actually a big problem on Android. My ex father-in-law literally had his bank account ripped off (£18000) from rogue app installed from outside the app store. And Google's stewardship of the play store is terrible. Note I'm mostly an Android user.
The fact that you have an anecdote does not make it a "big problem".
If you're side loading apps and entering banking credentials into them, that's a human problem, not a tech problem.