I went all out for my gramp's PC:

- Linux Debian with default user privileges

- XFCE kiosk mode with everything as shortcut icons (that can't be deleted) + removed all UI access to everything else

- Monthly Borg save of the /home dir

- X2Go for screen sharing when assistance required

So that's the great thing with Linux: you can make it look exactly how you want (huge icons, etc.), and you basically just save the /home dir to save the "state" for the user. Downside is that config is a lot of work.