LCD Display shows always squares [bad soldering]

Hello,
I have soldered the I2C with a typical 16x2 LCD display and I have this problem that it always shows squares.
I am not sure why it happens, but here is the code

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

// Set the LCD address to 0x27 for a 16 chars and 2 line display
LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {
  // Initialize the LCD
  lcd.init();
  
  // Turn on the backlight
  lcd.backlight();

  // Clear the display
  lcd.clear();
  
  // Set the cursor to column 0, line 0
  lcd.setCursor(0, 0); 

  // Print a message to the LCD
  lcd.print("Hello, World!");
  
  // Set the cursor to column 0, line 1
  lcd.setCursor(0, 1);
  
  // Print a second message
  lcd.print("I2C Tutorial");
}

void loop() {
  // Main loop does nothing
}

Any suggestions?

The squares indicate that the display is correctly powered, but I2C communications are not working.

To check communications, run the Arduino I2C address scanner program.

Just ran it and it says
I2C device found at address 0x27

Odd. Perhaps the display is nonfunctional. Please post a link to the product page.

I don't know what this means. What is "the I2C"?

I have soldered the I2C with a typical 16x2 LCD display

If you are talking about some sort of I2C LCD backpack, post a link to it, and check whether your soldering job is faulty.

Adjust the pot on the back, it may be working but washed out.

I do not have the exact page because it is quite old and their website is down, but I found identical product in this page

For the soldering I might post a photo, because this might be 2nd time I ever solder

The pot on the back, I have moved it several times, just changes the brightness, nothing else.

Your picture is not clear enough.
Please show a clear picture so we can evaluate your solderings.

Take a look at the product page you have postet - they show a decent and consistent soldering.
The solder points should shine, solder should be on both side of the mounting hole.

E and D0 seem to be shorted on your picture.
Redo your soldering.

Soldering is bad on several pins. Use hot iron (650-700) and liquid flux.

Thanks guys, I resoldered it and it worked.

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