dpkg-awk is a powerful general-query tool for Debian packages under APT. I'm pretty sure it can be applied to this problem.
apt-rdepends will show what packages depend on a given package:
A given package's own description will tell you what packages it depends on. That's just plain
apt show <packagename>
Hashtag your questions. They're much easier to find that way.
@dredmorbius not sure it was me but this is definitely something I have asked before.
It would be very nice to create a complete dependency graph such that you could find packages that are marked as manually installed and also not dependencies of other packages. These represent packages you can remove without breaking anything.
Maybe aptitude can be of help?
You can query for automatically installed packages (and manually by prepending it with '!') and also for dependency types.
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