Backspace doesn't work on Touchscreenkeyboard

I looked a lot of topics but don't found an answer. I have a code that working on WindowsEditor platform, but it's doesn't work on mobile device:

 if (Input.inputString != "")
 {
   _label.text = Input.inputString;
 
   if (Input.inputString == "\b")
     Backspace = true;
 }

So for mobile I write like this:

     if (_keyBoard.text != "")
     {
       _label.text = _keyBoard.text;
     
       if (_keyBoard.text == ...)
       Backspace = true;
     }

What I should to do here "_keyBoard.text == ..." ?