I haven't updated my Nexus 5X OS version for a long time already, due to the fact that I'm really afraid that something might go wrong with the state of some of my apps.
For example, my WhatsApp history goes back to 2011. The folder size is ~5GB and holds more than 29,000 files. A few times before the app produced a warning shich stated that its state is corrupted for some reason ("something went wrong") and that a restore is needed -- each time it took hours, and almost never succeeded immediately (I had to re-install and change some backup file names).
So, my question is basically -- what are the steps of the Android OS update installation process? Does all the apps being uninstalled, then the new version of the OS is being installed, and then the apps are being installed again? Or is there some "intermediate state" for the apps, which can provide an option for the apps not to be uninstalled in the first place?