Is it true that verses of the Holy Quran were revealed and then forgotten by the Prophet, peace and blessings be upon him, as a Christian priest claims, that Surat At-Tawbah was 200 verses, and what is the wisdom behind that if true, and why do Muslim scholars not address this issue?

A Muslim must safeguard their religion from doubts, and the prohibition of looking into the books of the People of the Book and listening to their doubts is even more severely forbidden. Abrogation (naskh) in the Quran does not necessitate bada’ (the emergence of a new opinion or knowledge after concealment), for Allah the Almighty is never preceded by ignorance nor does knowledge come upon Him anew; rather, He is All-Knowing of everything eternally and forever. Abrogation is proof of Allah's prior knowledge that the abrogated ruling suited a specific time for an interest that would conclude, and that the abrogating ruling would replace it at a known time for another interest. All of this was known to Allah in advance, and not an emergence of something new to Him. The wisdom behind abrogation lies in the gradual progression of the Shari'ah in educating the Ummah and nurturing it with what elevates it, such as the gradual application of rulings like the prohibition of intoxicants, or to lighten the burden on people out of mercy, or as a trial and test for Allah to distinguish the evil from the good.