ledcSetup was not declared in this scope

tried to point you to the Espressif documents that explain what are the differences between version 2.x and 3.x of the ESP32 API.

On 3.x version, ledcSetup() and ledcAttachPin() are no longer available. That means you have 2 options:

Rollback the version of the ESP32 board to the version 2.x OR modify your code according to the new API. Since the code is nor big or complex, I suggest the second option.

void setup() {
    ledcAttach(LEDC_PIN, 50, LEDC_RESOLUTION); 
}

and all ledcWrite functions thereafter will need to be:

ledcWrite(LEDC_PIN, dutyCycle);

LEDC

The LEDC API has been changed in order to support the Peripheral Manager and make it easier to use, as LEDC channels are now automatically assigned to pins. For more information about the new API, check LED Control (LEDC).