Hi,
On this page:

Installing the ESP32 Board in Arduino IDE (Windows, Mac OS X, and Linux)

There is this step:
4) Search for ESP32 and press the install button for the “ESP32 by Espressif Systems“:
Unfortunately, there is no Board Manager called “esp32 by Espressif System” listed. Perhaps the name has changed? Please let be know the correct Board Manager to install and update the course.
Thank you,
John