Did the same thing. Got them using FOSS apps on Windows (Firefox, LibreOffice, Thunderbird), then switched them and made Linux look like Windows. They never cared, kept on using it like nothing changed.

I started using FOSS apps on OSX until I got familiar with them, then moving to Linux was a lot easier.

Is the StumbleUpon thing not something Mozilla could do with Pocket?

I installed Ubuntu about 15 years ago and my Dad thought it was the new Windows. Had far fewer problems with it, but he kept hitting random keys and causing the most amazing errors. I just heard about EndlessOS which seems perfect for old folks.

https://www.endlessos.org/os

Piwigo.