NSLayoutConstraint — два элемента, одна строка, приоритет интервалов

Предоставление левой метке более высокого приоритета охвата контента должно помочь.

// In code
leftLabel.setContentHuggingPriority(.defaultHigh, for: .horizontal)

Для дальнейшего чтения по этой теме я нашел это очень полезным

Пример детской площадки

//: A UIKit based Playground for presenting user interface
  
import UIKit
import PlaygroundSupport

class MyViewController : UIViewController {
    
    override func loadView() {
        let view = UIView()
        view.backgroundColor = .white

        let leftLabel = UILabel()
        leftLabel.text = "I am left"
        leftLabel.backgroundColor = .orange
        leftLabel.translatesAutoresizingMaskIntoConstraints = false
        
        let rightLabel = UILabel()
        rightLabel.text = "I am right"
        rightLabel.backgroundColor = .yellow
        rightLabel.translatesAutoresizingMaskIntoConstraints = false
        
        view.addSubview(leftLabel)
        view.addSubview(rightLabel)
        
        leftLabel.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 16).isActive = true
        leftLabel.trailingAnchor.constraint(equalTo: rightLabel.leadingAnchor).isActive = true
        leftLabel.topAnchor.constraint(equalTo: view.topAnchor, constant: 16).isActive = true
        
        // This is the important part
        leftLabel.setContentHuggingPriority(.defaultHigh, for: .horizontal)
        
        rightLabel.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -16).isActive = true
        rightLabel.topAnchor.constraint(equalTo: leftLabel.topAnchor).isActive = true
        
        self.view = view
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()