I hear you. The problem is, that basically nothing stops you from building anything yourself. The difference is, that there is no easy-to-use build-in solution (like time machine) and ease of use is what makes the difference. Especially a TIME difference. Of course there is software SIMILAR to time machine, but it seems to be hard to write something rock solid and easy-to-use.
In fact I also have built it myself: https://github.com/sandreas/zarch A script that installs Arch on ZFS with ZFSBootMenu and preconfigurable "profiles" which packages and aurs to use. Support for CachyOS Kernel with integrated ZFS is on my list.
I already thought putting together a Raspberry PI Image that uses SSH to PULL backups over the network from preconfigured hosts with preconfigured root public keys and is easily configurable via terminalUI, but I did not find the time yet :-) Maybe syncthing just is enough...
Isn't the main point that you delegate curating and building the system image to the KDE project?
This is more about preventing the user from messing up their computer than it is about data safety.
I've been using Bazzite for 2 years now (an immutable distro based on Fedora Silver blue) and I just love the fact that I can "unlock" the immutability to try something that could mess up my systemd or desktop environment, and I can just reboot to erase it all away.
I also have a github action to build my custom image with the packages I want, and the configuration I want.
And this makes adding a backup setup even easier, it can be baked-in the distro easily with a custom image ! Your grandparents don't have to do anything, it will auto update and auto apply (and even rollback to the n-1 build if it fails to boot)