Hello Rafal,
That's a bit better.
I do not use the Nextion libraries so any help I can give will be limited. I am aware that the libraries from ITEAD are full of bugs, if you go to Ray Livingston's Nextion libraries you can download an improved version with most of the bugs removed.
I use debug to test HMI solution, work well. If i use debug with MCU input and my arduino, the debug send data to arduino, arduino do the tricks and send back data to debug screen. It work well.
I don't know what this means, sorry. The only debug I am aware of is in the Nextion editor and it doens't send data to an Arduino and it doesn't receive data from one either. You must be using something I am not aware of.
I get the impression from reading your post that you don't clearly understand the code you are using, is this true? Do you understand C/C++ at all? Do you understand the Nextion language and commands? The impression I have is that you are using a demonstration without understanding it. If this is the case you need to learn the basics first.
I have a tutorial on this site Using Nextion displays with Arduino , which might help you, but be aware that to use my methods you need to understand C (not necessarily C++) and some of the Nextion language. However, I can be a lot more helpful with my own methods than I can with the Nextion libraries.