Preservation Of The Quran
If you really want to dig deeper into the issue, I would request you to spend some time in reading both the articles posted above completely and watch the videos posted at the end of both threads. If you want to go straight down to the videos then I would recommend you to watch the following whole series based on 20 years of research of Dr. Shehzad Saleem, after that, if you have any further questions, you can freely ask them here. The playlist can be accessed at: https://www.youtube.com/playlist?list=PL3yXG2ufxd6Ufv8iDWTj_JGbICzfiyLoB As far as the seven recitations mentioned in Hadith, the words used in Hadith are not recitation (Qirat). No Hadith contains those words in it, some jurists/scholars did however misconstrue the word ‘Saba Ahraf’ in the meaning of Qirat (recitation).
Dr. Shehzad Saleem has also written a very detailed book about this subject after two decades of research: https://www.almawridus.org/bookstore/english/history-of-the-quran-a-critical-study/ A summary of this book is also available: https://www.almawridus.org/bookstore/english/history-of-the-quran-a-concise-study/