After a bit of trial and error I finally managed to recreate the ppa penguins-eggs-ppa repository.
This repository currently includes only the amd64 version, I don’t know the method to include also the i386 and ARM versions.
I think it’s not so difficult to create this repository with all architectures but, unfortunately, I’m not an expert in this field. If someone can help is, of course, welcome.
Copy and past the follow two lines:
curl -SsL https://pieroproietti.github.io/penguins-eggs-ppa/KEY.gpg | gpg --dearmor | sudo tee /usr/share/keyrings/penguins-eggs-ppa-keyring.gpg
sudo apt update
After that you can continue following the eggs official book.