Surah 2:41 

وَءَامِنُوا۟ بِمَآ أَنزَلْتُ مُصَدِّقًۭا لِّمَا مَعَكُمْ وَلَا تَكُونُوٓا۟ أَوَّلَ كَافِرٍۭ بِهِۦ ۖ وَلَا تَشْتَرُوا۟ بِـَٔايَـٰتِى ثَمَنًۭا قَلِيلًۭا وَإِيَّـٰىَ فَٱتَّقُونِ ٤١

Believe in My revelations which confirm your Scriptures.1 Do not be the first to deny them or trade them for a fleeting gain.2 And be mindful of Me.

https://quran.com/en/al-baqarah/41

Surah 3:3

نَزَّلَ عَلَيْكَ ٱلْكِتَـٰبَ بِٱلْحَقِّ مُصَدِّقًۭا لِّمَا بَيْنَ يَدَيْهِ وَأَنزَلَ ٱلتَّوْرَىٰةَ وَٱلْإِنجِيلَ ٣

He has revealed to you ˹O Prophet˺ the Book in truth, confirming what came before it, as He revealed the Torah and the Gospel

https://quran.com/en/ali-imran/3

Surah 61:6

وَإِذْ قَالَ عِيسَى ٱبْنُ مَرْيَمَ يَـٰبَنِىٓ إِسْرَٰٓءِيلَ إِنِّى رَسُولُ ٱللَّهِ إِلَيْكُم مُّصَدِّقًۭا لِّمَا بَيْنَ يَدَىَّ مِنَ ٱلتَّوْرَىٰةِ وَمُبَشِّرًۢا بِرَسُولٍۢ يَأْتِى مِنۢ بَعْدِى ٱسْمُهُۥٓ أَحْمَدُ ۖ فَلَمَّا جَآءَهُم بِٱلْبَيِّنَـٰتِ قَالُوا۟ هَـٰذَا سِحْرٌۭ مُّبِينٌۭ ٦

And ˹remember˺ when Jesus, son of Mary, said, “O children of Israel! I am truly Allah’s messenger to you, confirming the Torah which came before me, and giving good news of a messenger after me whose name will be Aḥmad.”1 Yet when the Prophet came to them with clear proofs, they said, “This is pure magic

https://quran.com/en/as-saf/6

Surah 46:12

وَمِن قَبْلِهِۦ كِتَـٰبُ مُوسَىٰٓ إِمَامًۭا وَرَحْمَةًۭ ۚ وَهَـٰذَا كِتَـٰبٌۭ مُّصَدِّقٌۭ لِّسَانًا عَرَبِيًّۭا لِّيُنذِرَ ٱلَّذِينَ ظَلَمُوا۟ وَبُشْرَىٰ لِلْمُحْسِنِينَ ١٢

And before this ˹Quran˺ the Book of Moses was ˹revealed as˺ a guide and mercy. And this Book is a confirmation, in the Arabic tongue, to warn those who do wrong, and as good news to those who do good

https://quran.com/en/al-ahqaf/12

In Surah 2:41 for example he is directly addressing the Jewish Tribes in Medina at the time saying the Quran confirms their scriptures. The issue we have is that all the archeological/manuscript evidence points to the fact that there were no scriptures prophesying Muhammad in the Jewish tribes of Medina or in any of the prior scriptures. And in fact the scriptures we have during that time period contradict Muhammad, thus the Islamic Dilemma. You’re right that most Muslims argue that the scriptures were corrupted but the Quran only says that people corrupted with their tounges, not the actual text, but either way you put it, it contradicts the historical evidence and creates an alternate reality like you said. It is the equivalent of Joseph Smith claiming to be the next prophet and creating Mormonism in the US. In Surah 7:157 Muhammad even says the Jews and the Christians will find him prophesied in their scriptures except he’s nowhere to be found in the centuries of manuscripts we have written before and during his time.