Can Allah forgive a young man who died in his twenties, who was a monotheist and believed in the existence and creatorship of Allah, but followed Deism and left Islam before his death? [Can He forgive him] by supplicating for him and giving Zakat on his behalf?

A deist is not considered a believer because faith necessitates belief in God, His books, and His messengers. Whoever disbelieves in any part of this is not a believer, as Allah Almighty says: "Indeed, those who disbelieve in Allah and His messengers and wish to differentiate between Allah and His messengers and say, 'We believe in some and disbelieve in others,' and wish to adopt a way in between—those are the disbelievers, truly. And We have prepared for the disbelievers a humiliating punishment." [An-Nisa: 150-151]. Modern deism is a form of contemporary atheism that denies revelation, prophethood, and religions.