Does anyone have any clue?

My best guess would be some relatively passive notification stealing focus.

As reddeadhead mentioned, there’s specific “don’t steal focus” settings. I’ve had good luck with them.

Immutable distros can usually be set to mutable with the correct privileged command.

It’s essentially security by obscurity. But I disagree with “no benefit”. An infection miss through dumb luck is still a miss, after all.

I used to always use Minecraft for this. Sure, they can’t do everything immediately, but I put the game on peaceful and let them explore at their own pace.

I say “used to” because Luanti (formerly MineTest, an open source Minecraft Clone*) is finished and free.

(Okay, Luanti is a lot more than a Minecraft clone. But for this discussion that’s all one needs to know.)

Nice. Minecraft used to be my go to answer for a first WASD game, too.

Lately, I recommend Mineclonia on Luanti, because it’s free and has stronger optimizations supporting weak laptops and big multiplayer servers. (It’s a popular Free Open Source Minecraft Clone).