Change the iOS keyboard layout to emoji?

Create a subclass of UITextField like this:

class EmojiTextField: UITextField {

    // required for iOS 13
    override var textInputContextIdentifier: String? { "" } // return non-nil to show the Emoji keyboard ¯\_(ツ)_/¯ 

    override var textInputMode: UITextInputMode? {
        for mode in UITextInputMode.activeInputModes {
            if mode.primaryLanguage == "emoji" {
                return mode
            }
        }
        return nil
    }
}

In Interface Builder select this class as the Custom Class in place of UITextField.

This causes the keyboard to select emoji keyboard, if available, when the field becomes first responder. The user can, of course, change the keyboard back to anything else at any time, but at least it gives an initial selection of what you want.

Thanks to blld for his answer here https://stackoverflow.com/a/58537544/1852207.