The Arduino -> Preferences page on my recent RPi4 sudo apt install Arduino installs do not have the Additional Boards Manager URLs field to enter the https://dl.espressif.com/dl/package_esp32_index.json address.
The first field on my Preferences pages is Sketchbook location: /home/pi/sketchbook
The first field on Bill's EXCELLENT Getting started with ESP32 example Preference page is
Sketchbook location: /home/dronebotworkshop/Arduino
I do NOT have a visible Arduino directory in my /home/pi/
I used sudo apt install rpi-imager, then sudo rpi-imager, and then did the update/upgrade,
followed by sudo apt install Arduino. What did I miss or foul up? MANY THANKS, in advance!
PROBLEM SOLVED!!!
DO NOT USE: sudo apt install arduino when installing an Arduino IDE on a Raspberry Pi !!!
This command installs an older default Arduino IDE that does not include the Additional Boards Manger URLs field and link.
DOWNLOAD the: Linux ARM 32 bits from Arduino.cc Software page and follow the instructions.
Many thanks to https://www.raspberrypi-spy.co.uk/2020/12/install-arduino-ide-on-raspberry-pi/