Mohammad was illiterate, which is why islamic writing was done by others to transcribe based on Mohammad’s recitations - the Koran. Why would an angel choose an illiterate man to write the word of God?
I’m not even certain that Muhammad was really illiterate.
According to Muslims, he was being raised by his uncle, he traveled as a merchant, delivering supplies to various communities.
He also traveled extensively with his first wife Khadijah, who hired him to help her with her trade business.
Surely there must have been some sort of written record kept to document these transactions. The merchant trade cannot exist without written records of what and how much was shipped to whom.