Drive ESP32-C3-DevKitM-1/ESP32-S2-Saola-1 on-board RGB LED (WS2812) in Arduino Framework, with Freenove WS2812 Lib for ESP32.

 According to Espressif documentation:

There is a on-board RGB LED (WS2812) on ESP32-C3-DevKitM-1, driven by GPIO8.
ref: https://docs.espressif.com/projects/esp-idf/en/v4.3.1/esp32c3/hw-reference/esp32c3/user-guide-devkitm-1.html

On ESP32-S2-Saola-1, the on-board RGB LED (WS2812) is driven by GPIO18.
ref: https://docs.espressif.com/projects/esp-idf/en/v4.3.1/esp32s2/hw-reference/esp32s2/user-guide-saola-1-v1.2.html

"Freenove WS2812 Lib for ESP32" is an Arduino library for WS2812 led on ESP32. To use this library, open the Library Manager in the Arduino IDE and install it from there.