Arduino IDE - Preferences - Additional Boards Manager URLs (esp32, esp8266, rtl87xx)
https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json
https://arduino.esp8266.com/stable/package_esp8266com_index.json
https://github.com/ambiot/ambd_arduino/raw/master/Arduino_package/package_realtek.com_amebad_index.json