Is it permissible to pray over a person who was born and raised a Muslim, then apostatized and died upon his atheism, and to attend his funeral and supplicate for him?

If your friend converted to atheism and died in that state, it is not permissible for anyone aware of his condition to pray over him, supplicate for him, wash him, shroud him, or bury him in Muslim cemeteries. This is based on Allah’s saying: (It is not for the Prophet and those who have believed to ask forgiveness for polytheists, even if they were relatives, after it has become clear to them that they are companions of Hellfire) [At-Tawbah/113]. And His saying: (And never (O Muhammad) pray over any of them who has died or stand by his grave. Indeed, they disbelieved in Allah and His Messenger and died while they were defiantly disobedient) [At-Tawbah/84]. And based on the saying of the Messenger of Allah, peace and blessings be upon him: (I asked my Lord for permission to ask forgiveness for my mother, but He did not grant it to me. And I asked Him for permission to visit her grave, and He granted it to me).