Programming

I'm completely with you

But I'm absolutely no familiar with modding since a long time and have no clue, if there would be many tutorials for Linux or if everything runs

I think Roblox e.g. doesn't run on Linux?

Minecraft was just possible with a different launcher, iirc.

I don't want to spend a day just setting up his environment - well, I do, but mostly for getting his system right. Getting stuck in something, that just maybe doesn't work in his environment is frustrating.

I went to a technical school and programmed micro controllers to make a running light or blinking Christmas trees
But that's just far too much, when he is only here for a week.

Here we call that "schnuppern".
Pretty much means sniffing, you just get the first taste of something.
Means, it should be a good experience.

So... Although I do like the idea, especially with Minecraft modding, I'm not sure if it's easily applicable

So currently I tend to the recommendation with the game "the farmer was replaced"
Reminds me of a challenge we had in our first week at the university, to just give an insight on logic and algorithmic thinking.
And as long as it works with Proton, it should just work and seems to step up the complexity, but still "gamecifact-ed"

I'll try to have a look at Minecraft modding, because maybe that's still cool - although he quit playing half a year ago or so - but I'll need to verify, that it works.
And sadly the planned week is months earlier than expected - I'm having 3 weeks and at least one of them I'll be on a business trip.

So, I need to keep it simple (read: just works) - and entertaining