However, while I love the approach of having an immutable distribution, I don't see the attack vector of ransomware handled in a good way. It does not help, if your OS is intact, but your data is irrecoverably lost due to a wrong click in the wrong browser on your system.
I think the backup and restore landscape has enough tools to fix this (cloud + restic[2] or automated ZFS snapshots[3]), but it takes a bit time / a script to setup something like this for your parents in your favorite distro.