I’m on Debian 12, KDE Plasma, I often get this error
E: The repository ‘cdrom://[Debian GNU/Linux 12.0.0 Bookworm - Official amd64 DVD Binary-1 with firmware 20230610-10:23] bookworm Release’ does not have a Release file. W: Updating from such a repository can’t be done securely, and is therefore disabled by default. W: See apt-secure(8) manpage for repository creation and user configuration details. E: cdrom://[Debian GNU/Linux 12.0.0 Bookworm - Official amd64 DVD Binary-1 with firmware 20230610-10:23] bookworm Release is not (yet) available (Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs) W: http://dl.google.com/linux/earth/deb/dists/stable/InRelease: Key is stored in legacy trusted.gpg keyring (/etc/apt/trusted.gpg), see the DEPRECATION section in apt-key(8) for details.
I didn’t install from a CD Rom or DVD, what is the problem here?
The sources.list contains a list of the sources that can be used for the installation and update of software packages. If you installed your Debian Linux distribution from a CD/DVD at some point, or maybe just by default if there is a CD/DVD player in your PC, an entry will have been added to the sources.list file corresponding to the mount point of the installation CD/DVD. Usually you can deactivate this entry after the initial installation, as I suppose that you further installs and updates will be from network sources. The full path to the location of the file is /etc/apt/sources.list. You can edit the file in a text editor, but as a newbie it is probably easier and safer to do that via your graphical update/package manager. Have fun discovering Linux.
For more information, have a look at: https://wiki.debian.org/SourcesList