Kerbal Space Program 1. I bought it in early beta for like $14, have received all subsequent updates for free because I bought it so early, sunk literally thousands of hours of enjoyment into it and come out with a solid basic understanding of orbital mechanics.
I cant think of a better return on investment I’ve ever made.
I tried this with my son, who is now 17 and not nearly as computer literate as I was by his age, let alone Linux literate at all. I think it’s a generational thing, as a kid growing up in the 90s I HAD to learn how to administer our PC at a higher level to do the things I wanted to do. Now with easy apps and tablets and auto-installation of all-the-things you just don’t need to be an advanced user to do what you want to do. This is just my experience, YEMV