It seems that I have! I see that it's the last button below credits, which is where the Exit button normally is.
Given that the game requires the tutorial to understand, and given its importance, I think there should be a popup like "Do you want to play the tutorial?" Yes (Recommended) vs Skip, when you press the Start button and you have detected that the player has not gone through the tutorial ever before.
I notice that a couple of others missed it too, so it seems I am not the only one, so making the tutorial more obvious would definitely help in the onboarding process :)