We are experiencing the same issue and confusion.
Whether we are creating a brand new project or existing project, the button has this new appearance (smaller corner radius).
The same is true for the SwiftUI equivalent button.
We are attempting to submit a feature using the button and Apple reviewers are suggesting that we are in violation of the guidelines.
This is catch 22. The guidelines state that we should use this component, but the same guidelines say that this component is invalid.