Dockerfile broken, no manual build possible

[Frobeniusnorm]

The dockerfile does not work.
At first, adding

RUN echo "deb http://security.debian.org/debian-security bullseye-security main contrib non-free" > /etc/apt/sources.list

at the top of the Dockerfile is necessary according to https://www.debian.org/security/.
However, it still won't install because of package conflicts.