Any one of the uBlue projects is perfect for this use case.

KDE: https://getaurora.dev/
Gnome: https://projectbluefin.io/
Gaming: https://bazzite.gg/

Install and setup once, run forever. Immutable so impossible to break for a non-tech user, no package upgrades fuck-ups because updates are atomic and don't touch the currently running system, are done in the background and are completely invisible for the user, great hardware support, based on Fedora. Regular users can only install Flatpaks through the App Store.

The only "maintenance" needed is a weekly reboot to move to the latest OS image.

As a personal feedback, I moved my gadget enthusiast but tech illiterate father on Bluefin. He can ruin a Mac in less than a few months. He can generate undocumented bugs on iOS by his mere presence. He hasn't touched the terminal in his life. But somehow, Bluefin is still running perfectly after a year and a half. That's how robust it is.

As a side note, passwords are extremely useful for basic security, and a password less life is extremely dangerous. The fact that you need to input a password tells you that you're doing something that requires extra care and attention.

If you're lucky to have a fingerprint reader that supports Linux (extremely rare unfortunately), you can get away with typing your password once at login and using your fingerprint for everything else.