Simpler is better in many cases. I have been using this messaging app for about a year now and I have been totally fine with it. It does what it says and it never connects to the internet unlike some Google ones.

1. Should have basic understanding of what they intent to do on Linux.
2. They should know about the concept of input devices.
3. Have an understanding of the internet if they are planing to use it. Like what websites are or how to search for things.
4. And I think a basic of generic buttons or symbols (like the magnifying glass for search button) would be nice.

For Fuck Sake its Free Software Foundation.

I 100% recommend bubblejail. A sandboxing utility based on bubnlewrap. The same that Flatpaks use I believe. It has a CLI and a GUI. And its super portable.

What you mean syncing with Gnome app?