Does the human skeleton recently discovered in the desert of Saudi Arabia, exceeding twenty meters in length, belong to the people of Ad, and is this considered evidence for the saying of the Messenger of Allah, peace and blessings be upon him, that the height of Adam, peace be upon him, was sixty cubits?

We have no knowledge of what you mentioned regarding the discovery of a trace in the Saudi desert. However, Al-Bukhari and Muslim narrated from the Prophet, peace and blessings be upon him, that Allah created Adam, and his height was sixty cubits, and that creation has been decreasing ever since. This news—if authentic—serves as evidence for what is stated in the Hadith, just as Allah Almighty said concerning 'Ad: "And He increased you amply in creation."