How do I know which provider AppCheck is using on iOS?

Question

I am currently developing an iOS application in which I have integrated AppCheck from Firebase. For iOS, AppCheck has the choice between two main providers: DeviceCheck and AppAttest. I understood that DeviceCheck was less secure than AppAttest so I made sure that AppAttest is correctly implemented in my project by following the Firebase documentation:

Steps followed on the documentation

And below is the code in my Xcode project

In MyAppCheckProviderFactory.swift :

class MyAppCheckProviderFactory: NSObject, AppCheckProviderFactory {
     func createProvider(with app: FirebaseApp) -> AppCheckProvider? {
          return AppAttestProvider(app: app)
     }
}

In AppDelegate :

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    // Override point for customization after application launch.
    
    // We define the attestation provider for AppCheck
    let providerFactory = MyAppCheckProviderFactory()
    AppCheck.setAppCheckProviderFactory(providerFactory)
    
    FirebaseApp.configure()
    
    return true
}

Here you can see that everything seems to work on the Firebase console:

Both providers are registered

User metrics

I know that normally the code I wrote above assures me that AppAttest is chosen but is there any way I can make sure that is the case?

Also I have created a DeviceCheck private key on my Apple Developper account, can I delete it? Note that I already have deleted the p8 file for DeviceCheck on Firebase as you can see here but the Key ID and Team ID fields are still filled in (as I had implemented DeviceCheck previously), can I also delete this without fear of affecting AppAttest. Is it so that the two providers are totally independent?

Finally, I have set the minimum iOS version allowed on my app to 14.0 (as AppAttest is only available from this version):

Like this in the Xcode project

What would happen if a user with iOS < 14 still managed to get my app?

Thank you very much for your attention and I wish you a nice day :) !