Linux From Scratch (LFS)[1] is well known but doesn't get a lot of fanfare. It was designed as a learning tool, but the avenues for exploration are endless.
LFS has the topic of package management covered quite nicely I think[1]. They describe the contraints and approaches that might be possible, and what the real world solutions to those are (PRM, DEB, et al).
There have even been some package managers designed (or at least discussions of what the design would look like) for LFS explicitly over the years, but none seemed to have come to fruition, and I can't find any links to them.
1: https://www.linuxfromscratch.org/lfs/view/9.0-systemd/chapte...
Edit: found the announcement https://www.gentoo.org/news/2023/12/29/Gentoo-binary.html