In short, my question is “Is there a way to prevent a non-malicious but unknowledgable and clumsy user to ruin their own home directory?”
Say my grandma opens a file browser looking for a picture, finds those dot files or those mysteriously-named directories distracting, sets her mind to deleting them. And assume she somehow finds a way to do so. While I understand that dot files or mysteriously-named directories of a non-privileged user are of no ultimate importance, it is a maintenance nightmare.
Plus, it’s not only mysterious files that are prone to be targetted. She might well delete by accident the picture she was looking for.
Two kinds of solutions that come to mind are: -Restrict file permissions in an adequate way -Implement an easily operable, fool-proof, back-in-time scheme
Is there a mainstream, well-supported distro of GNU/Linux that has figured this use-case out?
I figure it might come in handy when Window 10 is no longer supported and the reports of hacks keep coming in.
Backups are your friend. As others have said, just automate backing up to an external device.
It’s only part of the problem. How many times x hours will you spend restoring files and reconfiguring everything ?
Think like « the font bar has disappeared from the top menu on my libreoffice writer, help »
I don’t know. I set up a friend of mine who was a complete computer novice with Linux Mint on his laptop well over a year ago and he has not called me for support a single time, where he was regularly calling for help with Windows. People who are afraid of technology usually don’t go randomly clicking on stuff to see what happens. I’m pretty sure that grandma is safe. Plus, if you’re spending HOURS configuring a computer for an elderly person who likely won’t use it very often…you’re doing it wrong.
What I also do is create a complete backup of all of my computers to an external SSD with Rescuezilla on a semi regular basis, so I always have something to fall back to should the entire system or storage device goes belly up. 
I personally don’t store ANY data on any of my laptops. I use Nextcloud and sync the files I want access to on the go. The rest stays on my Nextcloud server at home.
If you are looking for a (mostly) fool-proof backup system that can restore changed settings and files even from a few minutes ago, you want macOS and Apple’s Time Machine. Pull out your wallet and hand it to Tim Apple.