Adversaries acknowledged Muhammad wrote the Quran

Even the prophet's adversaries among his contemporaries acknowledged that he could read and write. This is stated in the following verse.

[25:5] They also said, “Tales from the past that he wrote down; they were dictated to him day and night.”

(٥) وَقَالُوا أَسَاطِيرُ الْأَوَّلِينَ اكْتَتَبَهَا فَهِيَ تُمْلَىٰ عَلَيْهِ بُكْرَةً وَأَصِيلًا

1	waqālū	وَقَالُوٓا۟	And they said,
2	asāṭīru	أَسَـٰطِيرُ	“Tales (of)
3	l-awalīna	ٱلْأَوَّلِينَ	the former [ones] (people) / past generations
4	ik’tatabahā	ٱكْتَتَبَهَا	(which) he wrote it
5	fahiya	فَهِىَ	and [it]
6	tum’lā	تُمْلَىٰ	it is dictated
7	ʿalayhi	عَلَيْهِ	to him
8	buk’ratan	بُكْرَةً	morning / day
9	wa-aṣīlan	وَأَصِيلًا	and evening / night.”

In another verse, we see a similar claim made against the prophet, but this time, it specifies that they speculated a human was teaching him.

[16:103] We are fully aware that they say, “A human being is teaching him!” The tongue of the source they hint at is non-Arabic, and this is a perfect Arabic tongue.

وَلَقَدْ نَعْلَمُ أَنَّهُمْ يَقُولُونَ إِنَّمَا يُعَلِّمُهُۥ بَشَرٌ لِّسَانُ ٱلَّذِى يُلْحِدُونَ إِلَيْهِ أَعْجَمِىٌّ وَهَـٰذَا لِسَانٌ عَرَبِىٌّ مُّبِينٌ

Interestingly, the Quran never refutes the claim that the prophet "wrote"; instead, it only refutes the other claims that the Quran was tales from the past or that it was dictated to him by men.

[53:2] Your friend (Muhammad) was not astray, nor was he deceived. [53:3] Nor was he speaking out of a personal desire. [53:4] It was divine inspiration. [53:5] Dictated by the Most Powerful.

(٢) مَا ضَلَّ صَاحِبُكُمْ وَمَا غَوَىٰ (٣) وَمَا يَنطِقُ عَنِ ٱلْهَوَىٰٓ (٤) إِنْ هُوَ إِلَّا وَحْىٌ يُوحَىٰ (٥) عَلَّمَهُۥ شَدِيدُ ٱلْقُوَىٰ