curious how you move all packages over

One can copy the system using a tar backup, fix the mount pointd by changing the volume label (which identifies the mount point), and do a dist upgrade then.

I guess that's the best way to do it on a server. But for desktop systems, I now think it is better to make a list of manually installed packages, and to re-install the packages that are still needed from that list. This has two advantages:

1. One gets rid of cruft and experimental installs that are no longer needed, which is really important in the long term.
2. Some systems (I a looking at you GNOME) can break in an ugly way if doing an upgrade instead of a re-install. Very bad behaviour, but it can happen. (And this might answer the question whether Debian is more stable than Arch: Yes, as long as you don't upgrade GNOME).

And one more thing I do for the dot files:

Say, my home folder is in /home/hvb . Then, I install Debian 12 and set /home/hvb/deb12 as my home folder (by editing /etc/passwd). I put my data in /home/hvb/Documents, /home/hvb/Photos/ and sym-link these folders into /home/hvb/deb12. When I upgrade, I first create a new folder /home/hvb/deb14, copy my dot files from deb12, and install a new root partition with my home set to /home/hvb/deb14. Then, I again link my data folders , documents and media such as /home/hvb/Documents into /home/hvb/deb14 . The reason I do this is that new versions of programs can upgrade the dot files to a new syntax or features, but when I switch back to boot Debian 12, the old versions can't necessarily read the newer-version config files (the changes are mostly promised to be backward-compatible but not forward-compatible).

All in all this is a very conservative approach but it works for me with running Debian now for about 15 years in a rather large desktop setup.

And the above also worked well for me with distro-hopping. Though nowadays, it is more recommended to install parallel dual-booted distros on another removable disk since such installs can also modify grub and EFI setup, early graphics drivers and so on, even if in theory dual-boot installs should be completely independent... but my experience is that is not any more always guaranteed.

Another possibly quicker way to do this is a larger BTRFS disk and create subvolumes from snapshots and mount these. When the subvolumes are no longer needed, they can be deleted like any folder.