After the Quran's revelation, did the Prophet continue to be unlettered, or did he acquire the ability to read and write? Can you provide evidence for this?
Allah Has granted the Prophet Muhammad every knowledge which he did not know as we read in Quran ( And He Has Taught you every knowledge which you did not know) Sura 4, Verse 113.
The Prophet Muhammad (SAWA) was never unlettered but for the benefit of the message of Islam, he did not practice reading and writing in front of people to avoid giving a chance to the enmities of Islam to accuse him copying from previous religious books.(Sura Al-Ankabout, verse 48).
Wassalam.