What is the ruling on unintentionally stepping on the Mus'haf, and does this incur sin, knowing that the place was semi-dark and the Mus'haf was partially covered?

There is no sin upon you for what occurred, so long as it happened unintentionally, based on the words of Allah Almighty: "Our Lord, do not take us to task if we forget or make a mistake," and based on the words of the Prophet, peace and blessings be upon him: "Indeed, Allah has overlooked for my Ummah (community) mistakes, forgetfulness, and what they are coerced into."