The Linux Ship of Theseus

1. pick any distro and install it.

2. Then, without installing another distro over the top of it, slowly convert it into another distro by replacing package managers, installed packages, and configurations.

System must be usable and fully native to the new distro (all old packages replaced with new ones).

No flatpaks, avoid snaps where physically possible, native packages only.

EDIT: Some clarification on some of the clever tools brought up here:

chroot, dd, debootstrap, and partition editors that allow you to install the new system in an empty container or blanket-overwrite the old system go against the spirit of this challenge.

These are very useful and valid tools under a normal context and I strongly recommend learning them.

You can use them if you prefer, but The ship of Theseus was replaced one board at a time. We are trying to avoid dropping a new ship in the harbor and tugging the old one out.

It may however be a good idea to use them to test out the target system in a safe environment as you perform the migration back in the real root, so you have a reference to go by.

Easy: pick two similar distros, such as Ubuntu and Debian or Manjaro and Arch and go from the base to the derivative.

Medium: Same as easy but go from the derivative to the base.

Hard: Pick two disparate distros like Debian and Artix and go from one to the other.

Nightmare: Make a self-compiled distro your target.