$ sudo apt update
E: The repository 'cdrom://Ubuntu 20.04.2.0 LTS _Focal Fossa_ - Release amd64 (20210209.1) focal Release' 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.
Respuesta1
Abra Software y actualizaciones, en la pestaña Software de Ubuntu, desmarque Cdrom con Ubuntu 20.04 'Focal Fossa' en Instalable desde CD-ROM/DVD