apt update focal Release' does not have a Release file code example

Example 1: does not have a Release file. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details

apt-get update --allow-insecure-repositories

Example 2: the repository does not have a release file eoan

sudo sed -i -re 's/([a-z]{2}\.)?archive.ubuntu.com|security.ubuntu.com/old-releases.ubuntu.com/g' /etc/apt/sources.list