Bismillahir Rahmanir Raheem
بِسۡمِ ٱللهِ ٱلرَّحۡمَـٰنِ ٱلرَّحِيمِ ,

Br. Nouman Ali Khan summarizes and explains some basic counter arguments against Orientalist/ Conservative Christian allegations against the Textual Preservation of the Qur’an. I would suggest that Muslims read this book by Shaykh Mustafa Muhammad al ‘Azami and this book by Mufti Muhammad Taqi Uthmani [db] for an indepth and complete understanding on the preservation of the Qur’an.

wa Allaahu Alam.
[and God knows best].