在UINavigationBar左侧的"后退"按钮旁边添加另一个按钮

let customButton = UIBarButtonItem(title: "自定义", style: .plain, target: self, action: #selector(customButtonTapped))

let backButton = UIBarButtonItem(title: "后退", style: .plain, target: self, action: #selector(backButtonTapped))
let backButtonItem = UIBarButtonItem(barButtonSystemItem: .fixedSpace, target: nil, action: nil)
backButtonItem.width = -8 // 调整间距

navigationItem.leftBarButtonItems = [backButton, backButtonItem, customButton]

@objc func customButtonTapped() {
    // 自定义按钮点击事件处理
}

@objc func backButtonTapped() {
    // 后退按钮点击事件处理
}