I'm a huge Linux fan but "it just works" is not a phrase I'd use in the same paragraph as Linux. Try explaining to your grandma that she needs to open a terminal and run "sudo apt update && sudo apt upgrade"
Why would grandma do that when there's been an update manager service GUI for two decades?
Either set it to do upgrades in the background automatically or tell her to hit "Install updates" when she sees a notification about it. Ideally you'd click the checkmark that enables the former.
The great thing about Debian and Ubuntu LTS releases is that they're rock solid and nothing changes for like a decade or however long they're kept on life support.
It seems that you haven't used it in a long time then. You don't need to go the terminal to update the system. Mostly you get a message that there are updates for the system. You click it, click update all and your done.
Either set it to do upgrades in the background automatically or tell her to hit "Install updates" when she sees a notification about it. Ideally you'd click the checkmark that enables the former.
The great thing about Debian and Ubuntu LTS releases is that they're rock solid and nothing changes for like a decade or however long they're kept on life support.