What are the ways to determine the installed apps on an IOS/Android user's phone from the outside?

Question

Mobile development

Hello everyone, what are the ways to detect installed apps on an IOS/Android user's phone from the outside? From the site or from the application installed by the user, what rights are needed for this and is it possible at all? What is needed to determine if a user has a specific application?

Answer 1

An application can be made from android through the PackageManager, which requests the appropriate rights.
For iOS, in theory, you can do it too, but in fact it violates the sandbox and privacy policy.