Your choice of terminology leaves a bit to be desired. You can't have an outlet on an LCD. You might have a pictorial representation of an outlet, or you might have a value that relates to an outlet.
and above them I have 4 buttons
The picture shows the buttons below the "outlets".
In order to select I have to press the same button for 5 seconds.
Why? Is it because your code uses delay() and simply doesn't get around to checking the switch state often enough? Or, is it that the code is written to require holding the switch for 5 seconds, to prevent accidental changes?
If I press the third button it opens the third menu.. ecc ecc
No clue what this means. The arrangement of switches and "outlets" in the picture suggests a one-to-one relationship between switches and outlets. Why does the third switch do something different?
I tried to do the menu with the MenubackEnd library
Seems like a reasonable thing to do. Except for not posting the code, that is.
but it hasn't a function to go to a specific menu voice.
How can I do this job?
That depends, I would think, on what "this job" is.
Is there a better library that can do this?
Better than what? Using what criteria to define "better"?
Or some line code I have to add to my code?
My crystal ball says that you need to add this line of code to the start of loop():
Serial.print("I need to post my code");
If that doesn't help, perhaps a clue will have revealed itself.