The ‘Backports’ repository for Debian 12 has been retired now that Debian 13 has been released.
This will cause the following error when you try and update the packages or try to update AMP:
E: The repository ‘ bullseye-backports Release’ no longer has 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.
The easiest way to fix this is to switch to the Debian archive for this repository. Edit your /etc/apt/sources.list file:
sudo nano /etc/apt/sources.list
And find these lines:
deb http://deb.debian.org/debian bullseye-backports main
deb-src http://deb.debian.org/debian bullseye-backports main
And replace deb.debian.org with archive.debian.org such that the lines look like this:
deb http://archive.debian.org/debian bullseye-backports main
deb-src http://archive.debian.org/debian bullseye-backports main
Then press CTRL+O and CTRL+X to save and exit.
Now when you update your repositories with sudo apt update it should behave as normal.