You have full control over what is erased/unerased.
I write about the Lubuntu QA testcases on this thread, or what we perform in Quality Assurance of the Lubuntu system, and that includes an “Install using existing partition” which re-installs a system non-destructively.
I perform that upgrade roughly weekly on a system of my own (one running jammy or 22.04(.4); using the unreleased daily ISO I get the latest packages), installed on a single partition, and it achieves an update of the packages on it, plus I ensure no loss of my data (ie. my music still exists, as does my chosen music player - a non-standard player Lubuntu doesn’t install which will auto-reinstall with the non-destructive install method used).
You can control what is erased, and what is not erased, by the options you use - if you select the correct options. It’s easy to make a mistake, so backup your data in case you make a mistake.
Many options cause erasure; eg. Replace Partition will replace what is there with your new system & nothing survives.