How to correct Tab Bar height issue on iPhone X

"File inspector" from right of Xcode storyboard, enable Safe Area guide layout to support your app in iPhone

This post describes it really well.

Create a separate file with the following code:

extension UITabBar {
    override open func sizeThatFits(_ size: CGSize) -> CGSize {
        super.sizeThatFits(size)
        guard let window = UIApplication.shared.keyWindow else {
            return super.sizeThatFits(size)
        }
        var sizeThatFits = super.sizeThatFits(size)
        sizeThatFits.height = window.safeAreaInsets.bottom + 40
        return sizeThatFits
    }
}

For iOS 11.3 this worked for me:

func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    tabBar.invalidateIntrinsicContentSize()
}

On iOS 12.1 I've solved this issue by overriding safeAreaInsets in the UITabBar subclass:

class TabBar: UITabBar {
    private var cachedSafeAreaInsets = UIEdgeInsets.zero

    override var safeAreaInsets: UIEdgeInsets {
        let insets = super.safeAreaInsets
    
        if insets.bottom < bounds.height {
            cachedSafeAreaInsets = insets
        }
    
        return cachedSafeAreaInsets
    }
}

For iOS 13.0 onward,

class TabBar: UITabBar {
    private var cachedSafeAreaInsets = UIEdgeInsets.zero

    let keyWindow = UIApplication.shared.connectedScenes
        .filter { $0.activationState == .foregroundActive }
        .compactMap { $0 as? UIWindowScene }
        .first?.windows
        .filter { $0.isKeyWindow }
        .first
    
    override var safeAreaInsets: UIEdgeInsets {
        if let insets = keyWindow?.safeAreaInsets {
            if insets.bottom < bounds.height {
                cachedSafeAreaInsets = insets
            }
        }
        return cachedSafeAreaInsets
    }
}