I have an issue with the code for Submenu. Someone to help me ?

Good day.

As you are using same buttons you need to "tell the code" where you come from. So best solution is to have 2 bool variables to detect that.

 bool RightActive;
 bool LeftActive;

          if (Input.GetButton("LB") && RightActive==false)
          {
              valueText.text = "LB";
              LeftActive = true;
                                  
              if (Input.GetButton("RB")) 
              {
                      valueText.text = "RB after LB";
              }        
          }

         else 
        {
         LeftActive=false;
         }
          
          if (Input.GetButton("RB") && LeftActive==false) 
          {
              valueText.text = "RB";
              RightActive=true;
                                  
              if (Input.GetButton("LB")) 
              {
                      valueText.text = "LB after RB";
              }
          }
         else 
        {
         RightActive=false;
         }

Something like this. (Maybe i forget some condition but this is the idea. To prevent code to execute wrong if)

OR you can do 4 diferent if in the same level (not one inside other) the first detect the first clik and activate a bool, the second activate the submenu if the clik and the bool are true. The same for the other side.

Bye!!