How to output codes through demultiplexer 74LS138?

[PikaOrgil]

I can’t output my code through demultiplexer with this code. I can only control the select pins. ( THIS IS A coding section for my previous post)

int tDelay = 500;
int latchPin = A0;
int clockPin = A1;
int dataPin = 13;

int buttonPin1 = 2;
int buttonPin2 = 3;
int buttonPin3 = 4;
int buttonPin4 = 5;
int buttonPin5 = 6;
int buttonPin6 = 7;
int buttonPin7 = 8;
int buttonPin8 = 9;

int A = 12;
int B = 11;
int C = 10;

byte leds1 = 0;
byte leds2 = 0;
byte leds3 = 0;

bool button_old1 = true;
bool button_old2 = true;
bool button_old3 = true;

bool button_new1;
bool button_new2;
bool button_new3;

void updateShiftRegister()
{
  digitalWrite(latchPin, LOW);
  shiftOut(dataPin, clockPin, LSBFIRST, leds1);
  shiftOut(dataPin, clockPin, LSBFIRST, leds2);
  shiftOut(dataPin, clockPin, LSBFIRST, leds3);
  digitalWrite(latchPin, HIGH);
}

void setup()
{
  pinMode(latchPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  
  pinMode(buttonPin1, INPUT);
  pinMode(buttonPin2, INPUT);
  pinMode(buttonPin3, INPUT);
  pinMode(buttonPin4, INPUT);
  pinMode(buttonPin5, INPUT);
  pinMode(buttonPin6, INPUT);
  pinMode(buttonPin7, INPUT);
  pinMode(buttonPin8, INPUT);
  
  pinMode(A, OUTPUT);
  pinMode(B, OUTPUT);
  pinMode(C, OUTPUT);
  updateShiftRegister();
}

void loop()
{
  button_new1 = digitalRead(buttonPin1);
  button_new2 = digitalRead(buttonPin2);
  button_new3 = digitalRead(buttonPin3);
  if(button_new1 != button_old1) 
  {
    digitalWrite(A, LOW);
    digitalWrite(B, LOW);
    digitalWrite(C, LOW);
    if(button_new1 == false)
    {
      leds1 = leds1 << 1;
      if(leds1 == 0b00000000)
      {
        leds1 = 0b00000001;
      }
      updateShiftRegister();
    }
    button_old1 = button_new1;
 
  delay(tDelay);
  }
 
  if(button_new2 != button_old2)
  {
    digitalWrite(A, HIGH);
    digitalWrite(B, LOW);
    digitalWrite(C, LOW);
    if(button_new2 == false)
    {
      leds2 = leds2 << 1;
      if(leds2 == 0b00000000)
      {
        leds2 = 0b00000001;
      }
      updateShiftRegister();
    }
    button_old2 = button_new2;
 
  delay(tDelay);
  }
  
  if(button_new3 != button_old3)
  {
    digitalWrite(A, LOW);
    digitalWrite(B, HIGH);
    digitalWrite(C, LOW);
    if(button_new3 == false)
    {
      leds3 = leds3 << 1;
      if(leds3 == 0b00000000)
      {
        leds3 = 0b00000001;
      }
      updateShiftRegister();
    }
    button_old3 = button_new3;
 
  delay(tDelay);
  }
}

[PikaOrgil]

Here’s the circuit picture

[lastchancename]

OPs pictures

[lastchancename]

Your schematic is straight out of the 1970s
To manage a string of LEDs like that today - I'd be looking at a string of 74HC595, or if more power is needed TPIC595's will drive bigger loads. or even WS28xx serial RGB LEDs would be easier than all that hardware.
3-wires for all those LEDs instead of 7 as shown