Best way to reinstall ubuntu?

Question

ubuntu

Ubuntu has been living on my home machine since version 8.04. Every half a year, it was successfully updated with the help of the distr-upgrade command.
I want to install the system from scratch in order to clean it from possible old bugs and packages that were left from the old versions of the operating system. Naturally, there is no desire to set everything up again and remember which packages and from which repositories I installed.
I have a hamster on the hotel partition, so the first problem is relatively easy to solve (just don't format it).
But what about the list of packages and repositories? I know that it is possible to save a list of installed packages to a file and then install all packages from that file. But, firstly, what to do with packages that will be obsolete in the new ubuntu (why should I install them if they are no longer needed?), and, secondly, what to do if any packages are missing?
Another possible "trick" is that I have a hamster (and another partition with multimedia) created on top of LVM. Can the latest ubuntu correctly identify them or will dances with a tambourine be needed? But, in principle, I'm most interested in how to install only the necessary packages? With LVM, I think I'll figure it out somehow.

Answer 1

dpkg --get-selections >myselections
dpkg --set-selections <myselections
There will be no major problems with software versions, since only the package name is stored.