New packages will be installed if required to satisfy dependencies, but existing packages will never be removed.
If an upgrade for a package requires the removal of an installed package the upgrade for this package isn't performed.
Failed to fetch http://security/debian.org/… 404 not found [IP: 146.75.118.132 80]
$ sudo apt upgrade
Do you want to continue? [Y/n] Y
Err:1 http://security.debian.org/debian-security bullseye-security/main amd64 libx11-xcb1 amd64 2:1.7.2-1+deb11u1
404 Not Found [IP: 146.75.118.132 80]
Err:2 http://security.debian.org/debian-security bullseye-security/main amd64 libwebkit2gtk-4.0-37 amd64 2.40.3-2~deb11u1
404 Not Found [IP: 146.75.118.132 80]
Err:3 http://security.debian.org/debian-security bullseye-security/main amd64 libjavascriptcoregtk-4.0-18 amd64 2.40.3-2~deb11u1
404 Not Found [IP: 146.75.118.132 80]
Err:4 http://security.debian.org/debian-security bullseye-security/main amd64 thunderbird amd64 1:102.13.0-1~deb11u1
404 Not Found [IP: 146.75.118.132 80]
E: Failed to fetch http://security.debian.org/debian-security/pool/updates/main/libx/libx11/libx11-xcb1_1.7.2-1%2bdeb11u1_amd64.deb 404 Not Found [IP: 146.75.118.132 80]
E: Failed to fetch http://security.debian.org/debian-security/pool/updates/main/w/webkit2gtk/libwebkit2gtk-4.0-37_2.40.3-2%7edeb11u1_amd64.deb 404 Not Found [IP: 146.75.118.132 80]
E: Failed to fetch http://security.debian.org/debian-security/pool/updates/main/w/webkit2gtk/libjavascriptcoregtk-4.0-18_2.40.3-2%7edeb11u1_amd64.deb 404 Not Found [IP: 146.75.118.132 80]
E: Failed to fetch http://security.debian.org/debian-security/pool/updates/main/t/thunderbird/thunderbird_102.13.0-1%7edeb11u1_amd64.deb 404 Not Found [IP: 146.75.118.132 80]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
Change from fullseye to bookworm (this is in late 2023).
Likely, sudo apt edit-sources should be used…
$ sudo sed -i s/bullseye/bookworm/ /etc/apt/sources.list
Update the package index:
$ sudo apt update
Then:
$ sudo apt upgrade --without-new-pkgs
Then also?
$ sudo apt full-upgrade