My navigation bar's large title is too wide. How to fix that?

This is the workaround that I found

override func viewDidLoad() {
  super.viewDidLoad()

  title = yourTitle
  adjustLargeTitleSize()
}

extension UIViewController {
  func adjustLargeTitleSize() {
    guard let title = title, #available(iOS 11.0, *) else { return }

    let maxWidth = UIScreen.main.bounds.size.width - 60
    var fontSize = UIFont.preferredFont(forTextStyle: .largeTitle).pointSize
    var width = title.size(withAttributes: [NSAttributedStringKey.font: UIFont.systemFont(ofSize: fontSize)]).width

    while width > maxWidth {
      fontSize -= 1
      width = title.size(withAttributes: [NSAttributedStringKey.font: UIFont.systemFont(ofSize: fontSize)]).width
    }

    navigationController?.navigationBar.largeTitleTextAttributes =
        [NSAttributedStringKey.font: UIFont.boldSystemFont(ofSize: fontSize)
    ]
  }
}

This question is somewhat answered here: How to resize Title in a navigation bar dynamically.

self.title = "Your TiTle Text"
let tlabel = UILabel(frame: CGRectMake(0, 0, 200, 40))
tlabel.text = self.title
tlabel.textColor = UIColor.whiteColor()
tlabel.font = UIFont(name: "Helvetica-Bold", size: 30.0)
tlabel.backgroundColor = UIColor.clearColor()
tlabel.adjustsFontSizeToFitWidth = true
self.navigationItem.titleView = tlabel

That being said, this is slightly different, in that you have the prefersLargeTitle property set. Now, I am not sure whether the tlabel.adjustsFontSizeToFitWidth = true overrides the prefersLargeTitle property, but try it out and see if it works. There is also some additional information regarding navigation item large titles here: https://developer.apple.com/documentation/uikit/uinavigationitem/2909056-largetitledisplaymode. Hope this helps.