The API does not expose this nor do I think it is possible.
According to the app store review guidelines - https://developer.apple.com/app-store/review/guidelines/
(vii) SafariViewController must be used to visibly present information to users; the controller may not be hidden or obscured by other views or layers. Additionally, an app may not use SafariViewController to track users without their knowledge and consent.
You can optionally pass in the "External" flag and it will just launch the default browser instead of using the SafariViewController.