I bought Minecraft when it was first purchaseable. Only converted my account last month as my new-school-entrant kid has asked what it is.
And honestly, I wish I didn’t. The MS launcher is an absolute shit show in usability for adults, let alone kids. Next time it forces me to log back in I’m just pirating it.
I bought two copies, I’ll fucking run them how I please.
I doubt it’s /just/ smoke ventilation. Sure, it’s primarily there for fire safety.
But it probably provides ambient ventilation for the tunnel too. Tunnels with trains get hot. Most things, living or inanimate don’t like heat.
And if it’s always ventilating, it’s also might be expelling brake and metal dust from passing trains.
But all speculation. I’m not a train engineer, so I’m probably wrong.