How sound is the saying that Prophet Muhammad (peace be upon him) left no footprint on the dust, while he did leave one on stones, and is this considered a miracle for him?

The fundamental principle is that the Prophet, peace and blessings be upon him, possessed human characteristics. There is no evidence that his trace would not appear on the ground or that it would be imprinted on stones but not on other surfaces. On the contrary, it is well-established that the polytheists tracked his footsteps during the Hijra (migration). If the matter were as stated, it would have been widely known and mentioned in books of biography and Hadith. Therefore, what the questioner mentioned is not established Islamically.