Is a person's death the result of an oppressed person's supplication, or is it a decree and destiny written before we were created?

If the oppressed person supplicates against the oppressor for death or otherwise, Allah may answer their supplication, due to the Prophet's (peace and blessings be upon him) saying to Mu'adh: "Beware of the supplication of the oppressed, for there is no barrier between it and Allah." This is part of Allah's divine decree and destiny. As for the supplication of someone who is not oppressed, it will not be answered because it is a supplication involving sin and aggression, due to the Prophet's (peace and blessings be upon him) saying: "The supplication of a servant continues to be answered as long as he does not supplicate for a sin or cutting off ties of kinship."