What is the agreed upon and what is disagreed upon concerning the Qur'an, disregarding the differences in readings?

Muslims have unanimously agreed that Allah has preserved the Qur’an from addition and subtraction, in accordance with His saying, the Most High: "Indeed, it is We who sent down the Dhikr (the Qur’an), and indeed, We will be its guardian" (Quran 15:9). The Qur’an has been transmitted to us through an unbroken chain of transmission (tawatur), generation after generation. They also unanimously agreed that whoever claims that the Book of Allah contains something not from it, or that anything has been removed from it, is a disbeliever.

The difference of opinion among scholars regarding whether the Basmalah is an ayah (verse) of the Qur’an does not disrupt the preservation of the Qur’an. The Companions agreed on its inclusion at the beginning of all surahs except Surah At-Tawbah. And one who affirms it or denies it does not become a disbeliever due to the scholarly difference of opinion concerning it. It has been said that the difference in counting the Basmalah as a verse of the Qur’an is like the variations in readings (qira’at) for some words and letters, where something might be affirmed in some readings that is not affirmed in others.