ARCore Instant Preview with white Screen

Hello everybody,

at the moment i try to connect my iPhone XS to my Mac (or even windows with itunes) to preview my ARCore App. So i followed this steps for the HelloAR sample:
https://developers.google.com/ar/develop/unity/quickstart-android
I didn't build the app because it is set to Andorid and not iOS. I just want to use the iPhone as a preview device.

So I also followed:
https://developers.google.com/ar/develop/unity/instant-preview

i can run the project on on my mac and windows computer. I also connected my iPhone XS with the Unity remote 5 App open. If i hit play, the iPhone receives the data from unity and i can see it in the unity remote 5 app. But instead of seeing the camera in the background for the AR functions, i only get a white screen in unity and on my iPhone.
I don't have any errors. Just the message:

Instant Preview version 1.12.0
To disable Instant Preview in this project, uncheck 'Instant Preview Enabled' under 'Edit > Project Settings > ARCore'.

There ist no difference if i set the target platform to iOS or Andorid.
Does anyone know where the problem is? Or do I have to use an Andorid Phone?

Thank you!