Ok, So what about the Wire.begin before your begin for serial ports?
u8x8.begin(); // Initialize OLED display
u8x8.setFlipMode(1);
u8x8.setFont(u8x8_font_chroma48medium8_r);
**Wire.begin();**
Serial.begin(115200); // Initialize serial communication
pinMode(LED_BUILTIN, OUTPUT); // Set LED pin as output
digitalWrite(LED_BUILTIN, HIGH); // Turn off LED