Believe me I tried that many times, with many people. At some point one just can’t adopt neither Linux nor windows, or macOS.
If you absolutely want a computer, because of special needs or a specific use case, you may find inspiration anyway from some half baked attempts of manufacturers to build an senior friendly OS and hardware. Overpriced and designed by people not knowing what they were doing, at least it was like they a decade ago.
I’ve been there too, the best success I had was :
An IBM (now Lenovo) laptop because strong as a tank, yes it did fall a couple of times.
Debian with a non root account.
A printer, yes, there will be screenshots and whole websites prints, because it reads better and it doesn’t run away when you inadvertently drag and click the mouse
FVWM95 because windows 95-98-vista desktop is what one did actually saw on TV series and movies.
BIG FONTS, zoomed views by default nowadays I would go for a wide screen.
Everything, every clickable item or icons removed from the start menu but internet, mail, print, remote help, power off. No word processors, no games, no calculator nothing. Mail IS the word processor. Excel is the good old desktop calculator sitting just there.
Exactly same icons internet, mail, print, remote help, power off icons on the desktop matching the start menu.
« Mail » was a shortcut to yahoo mail. Nowadays there may be better options.
Remote help: this was a VNC server in teacher - school mode, to connect my computer (teacher) and grant me remote hands with nothing more (not event the local IP, or the teamviewer session ID…) because when this icons was clicked it was already a panicky situation there.
Internet: at that time it was Firefox with all plugins, a custom home page with mail and google , same thing on the shortcut bar. A windows 95 skin and read only (chmod) on some config files so it wouldn’t be broken (again accidental mouse drag and click will wreak the interface, removing or adding one bookmark, accepting a ad for a new search engine that will replace the default search engine).
…
Omg I started typing and now I remember how difficult it was technically and how hard it was to help people trying to be a decent human being every single time. Everything will break in a way neither you nor the user could imagine or understand how it happened clearly.
Android is already too soft and customizable unfortunately