What is the Islamic perspective on divine decree (Qadaa) and destiny (Qadar)? Can a person control their fate, or is it predetermined, considering that Allah is All-Knowing of everything, even what has not yet occurred, for instance, in an attempt to treat and save someone from death?

Everything is written and predetermined, as stated in the Holy Quran and the Prophet's Hadiths. This predetermination is hidden from us, and we must not rely on it and abandon work and taking means. There is no contradiction between the two. Allah has given us will, ability, choice, and volition, yet we do not step outside of Allah's power and will. There is no contradiction between attempting to save a person from death and Allah's predetermined and written decree, which we only know after it occurs.