Solved.
Apparently this is not the first time this has happened to contabo and a few years ago I found a message on this forum.
Apparently the mirrors don’t keep them up to date, and someone with little experience like me can have a hard time.
The solution is to edit the file: /etc/apt/sources.list
Delete everything else related to contabo and add the “official” sources:
deb http://deb.debian.org/debian bullseye main contrib non-free
deb-src http://deb.debian.org/debian bullseye main contrib non-free
deb http://deb.debian.org/debian-security/ bullseye-security main contrib non-free
deb-src http://deb.debian.org/debian-security/ bullseye-security main contrib non-free
deb http://deb.debian.org/debian bullseye-updates main contrib non-free
deb-src http://deb.debian.org/debian bullseye-updates main contrib non-free
Anyway I will send a ticket to contabo to get it fixed.
Have a nice day