going down the ios route is safest option.Pretty much in same boat as you taught my dad on online bill payments and banking in iPad . Set up a password manager and store all their personal information in there , make it available via touch id. Chromebook and linux are still tech stuff which can not be handled by elderly.

iOS/macOS with 1blockerX/1blocker and keychain has worked wonders for my parents.

I’d say use AdGuard instead of 1Blocker - the latter pretty much never updates its blacklists.

Ublock Origin by gorhill is better, although the trouble with any ad-blocking plugin being used by non-technical people is that they will occasionally break a site and have no clue how to turn it off.

This is for iOS though, where JavaScript-based plugins like uBlock don’t work (and in fact JS-based plugins are deprecated on desktop Safari as well).