IOS App UI Design Best practices

Top Bar, do you mean status bar ? or Navigation bar ?
What do you mean by bottom bar ? Is it the TabBar ?

Status bar are not required.
There is even an API to hide status bar:

Code Block 
override var prefersStatusBarHidden: Bool {
    return true
}

And navigation bar are needed only if you have a navigation view.

I'm not even sure it is a best practice. Where did you read this ?

So, don't worry about this. And only use top or bottom bar if that allows for better use of your app.

And read this carefully, you'll learn a lot on user interface design.
https://developer.apple.com/design/human-interface-guidelines/ios/overview/themes/

Thanks a lot for reply , I mean Top Navigation bar , bottom TabBar . I think you believe it's not must ?