Did the Qur’an first descend upon the angels in Bayt al-’Izzah, after Gabriel heard it all at once from Allah, and then Gabriel descended with the verses upon the Messenger (peace be upon him) according to the events and occurrences?

The Quran was sent down all at once from the Preserved Tablet to the House of Glory (Bayt al-Izzah) in the lowest heaven. Then, Jibreel (Gabriel), peace be upon him, brought it down to the Prophet, peace and blessings be upon him, in parts. Jibreel had heard the Quran directly from Allah Almighty before descending with it. It is not permissible to ponder over the 'how' of these unseen matters for which no detailed explanation has been provided in revelation. Rather, one must believe in them as they have been revealed.