FocusState | Apple Developer Documentation
A property wrapper type that can read and write a value that SwiftUI updates as the placement of focus within the scene changes.
Use this property wrapper in conjunction with focused(:equals:) and focused(:) to describe views whose appearance and contents relate to the location of focus in the scene.
In the following example of a simple login screen, when the user presses the Sign In button and one of the fields is still empty, focus moves to that field. Otherwise, the sign-in process proceeds.