And then add the repository to your sources list:
sudo sh -c 'echo "deb [arch=amd64,arm64] http://repo.ros2.org/ubuntu/main `lsb_release -cs` main" > /etc/apt/sources.list.d/ros2
I’m curious why you suggest setting up multi-arch sources right out of the gate? I can’t imagine that will often work well unless the rest of the sources are also setup to be multi-arch, which isn’t discussed there. Even then, why suggest it by default?