ESP32 Software Serial library issue

Hello Rui /Sara
I was having a problem with building the software for this project in VScode/Platformio.  I have used this Platformio with Arduino extension many times in my various projects with the ESP32, and have not had any issues with the serial ports.
Creating the project in Platformio and entering the code from page 47/48 of the pdf, when building an error resulted: ” \SoftwareSerial.cpp:42:27: fatal error: avr/interrupt.h: No such file or directory”.    This was resolved (I think…) by finding an EspSoftwareSerial library in the Arduino libraries and copying (renaming it to SoftwareSerial) this to the .platformio/lib/SoftwareSerial folder.  After this, the build worked and downloading to the ESP32 resulted in a connection the Firebase db as per the pdf. (and the serial monitor worked).
Just wondering if you any idea why this happened?
Many thanks in advance, and I am enjoying your work on this project.
Best Regards,
Paul Smulders