A similar feature request is opened for react-native-app-auth. Not sure if this has to be done there as well, before it could be managed in expo.

Using ASWebAuthenticationSession will automatically present a mandatory dialog box asking the user to give explicit consent for accessing the website’s data. This consent screen shows product and domain name. Our customers are always irritated, what this will mean. New customers also immediately leave the app. Because there is no way to describe that the data is not shared with 3rd parties. iOS 13 may omit the dialog by configuring ASWebAuthenticationSession for a private session using the new prefersEphemeralWebBrowserSession parameter, which needs to be set before start is called.