This is how the steam deck works. I think newer android phones do this too.

that is one way to do it, and it's a very common one - it's robust and simple. So I can't correct you, but thought I would add to it. In NixOS, they've improved it by making sure all your apps are symlinked, and when updating, these symlinks are updated. That way you can start using your newly updated system straight away, without a reboot. When rebooting, you are prompted to which generation you want to boot into, (defaulting to "latest" after a few seconds of no input) making rollbacks a breeze.

That sounds kinda like what any OS should do in the history of OSs...