There are many problems with the claim the Quran is preserved here is a summary:
1. The Quran was only put as one book 20 years after Muhammad died!! Before that, it was scattered as scrolls written on stones, leather, and bits of papers! This opens a can of worms as to why Muhammad or Allah never asked for the book to be collated before Muhammad died! (I have another post about that!)
2. The four scribes (even the hadith cannot agree in their names!), did not survive. How can we trust a no body by Zaid Ibn Tabith to remember 114 chapters with 6,350 verse in the correct order? He is no Prophet, Khalifa, Iman…no body!!
3. Too many repetitions that do not make sense until you realise Muhammad was getting old and forgetful as the authentic hadith says in multiple places:
4. Narrated Aisha: The Prophet heard a man reciting the Qur’an in the mosque and said, “May Allah bestow His Mercy on him, as he has reminded me of such-and-such Verses of such a Surah.”
Sahih Bukhari 6:61:556
Repeated in: Sahih Muslim 4:1720
And Quran 87:6:
We will have you recite ˹the Quran, O Prophet,˺ so you will not forget
4.Islamic source confirm that the caliph Uthman ordered various copies of the Qur’an to be burnt because there were clear differences in the Qur’ans among people of Sham and people of Iraq. The differences were so great Uthman and his companions feared future dispute. Uthman asked Hafsa for her copy and he ordered to make many copies and destroy all the other copies. This shows that memorization had failed to completely preserve the Qur’an.
5. The compilation of the Qur’an was clearly a very human process involving trial and error, educated guesses, faulty memories, fallible opinions, disagreements, mistakes, ignorance, and bad decisions. And we can’t forget, of course, the pile of manuscripts reduced to ashes by Uthman in his desperate attempt to destroy all evidence that the Qur’an hadn’t been perfectly preserved. The early Muslim community left modern Muslims with a huge mess to clean up if they want to cling to the belief that the Qur’an was perfectly preserved as you can see in these hadiths: https://sunnah.com/muslim:1050