I recently downgraded the Xamarin-iOS package to 15.0.0.6.pkg to fix this known issue:

How to overcome "Please select a valid device before running the application." on a paired with Mac Visual Studio on Windows 10

The fix worked for the connection to an iPhone. But since I need to access the filesystem, it's easier to do it with the simulator.

The app needs access to the phones keychain to start correctly. When I tried to start with the simulator I got a NullReference Exception because the keychain could obviously not be accessed.

The provisioning profile used was: Provisioning Profile: "VS: WildCard Development"

I have no idea what to do next. Anyone has an idea?