Ooooh this explains the situation perfectly, including why I am unable to reproduce this. It is not your tor mirror. What you see happens because you told apt to do two things:
- keep systemd at version
257.7-1 - upgrade everything
With those constraints, the only way apt found to satisfy both was to uninstall a lot of stuff because the stuff it otherwise would upgrade was incompatible with keeping systemd at version 257.7-1.
After removing the constraint of keeping systemd at version 257.7-1 you can see that one of the things that apt wants to do is upgrade it. Without upgrading it, you cannot upgrade other packages.
So no, this is not a bug in apt but a result of what you tell apt with the contents of your /etc/apt/preferences.d/apt-listbugs.
Maybe investigate whether the bugs for which you installed the pinnings are still relevant and if not, remove the pinning and then you can upgrade while only removing reform-firedecor.