Just install a friendly Linux distro and relax
Everyone saying "well they shouldn't be installing anything, lock them down" should really be saying "just buy them an iPad".
inb4 eclipse uninstalls windows wireless drivers.
My non-techie father has been using an Ubuntu 1604 LTS workstation for years with no trouble.
Additionally, peppermint os was designed around a web-centric OS experience some time before chromebooks became a thing: https://peppermintos.com/guide/ice/
Finally, Chromebooks. Got one for my wife, who is about as computer illiterate as it gets (only computer she'd previously owned was a mobile phone) and it Just Works for her. Aside from being pretty locked down, it's about as friendly of a linux OS as linux gets.
This is a core point. We've reached the point that for common users, the OS doesn't matter anymore. Browser, video player, image viewer, word processor... BOOM! Done!
I think this is why there' such a push toward cloud-based subscription services because OSes (a decade from now?) will be the modern equivalent of a locked-down dumb terminal.
It's part of the reason, I'm convinced, that Microsoft went Chromium. Even the browser doesn't matter. It's just a face... a front-end to a search engine, subscriber-based online apps and targeted tracking.
Remember that sometimes grandma manned a crew-served grenade launcher.