If you do go for a smartphone, my experience tells me that there's no difference between Android and iOS. The biggest sources for shady apps are the Google Play Store and Apple App Store. Shady stuff on the web can be easily defeated using an adblocking browser, which is essential for older relatives.
You know, they are adults and have free will and do want a smartphone like everyone else to use Whatsapp, read the news, search things on Google, etc.
Hell, my 95 year old grandma convinced a nurse to install TikTok on her phone because she saw her using it and also wanted to try it. It's not like we can isolate them from the world
With a well-supported hardware configuration and a working web browser, even a non-techie may have a more stable experience than they would with Windows.
That has as much to do with the decline of Windows as with the ascent of desktop Linux, but still.
Bulletproof, immune to all the apps and malware. She couldnt break it.
A Linux install that meets the basic needs of the user is perfecto!
Less so recently just due to time constraints, but I'm generally the technical person in my family group, and I've lost enough touch with Windows that troubleshooting it is increasingly difficult. If they need me to 'format and reinstall' they're getting Linux unless they have a very specific need that only Windows can cater to.