General ACCAbook an exam for September session

Short answer - no. See https://www.accaglobal.com/vn/en/student/getting-started/important-dates.html the late exam entry deadline was Monday 8th August - for an applied skill exam it would have cost you £339 rather than the standard entry fee of £132. Deadlines are deadlines - ACCA has to appoint exam supervisors/proctors/administrators etc based on candidate registrations and can make no exceptions.

Do the same deadlines apply to on-demand CBEs, or only the session exams?

@lynnkhatib Welcome to our forums - on-demand is on-demand so doesn't need such deadlines. For ondemand you are booking with a centre or to sit remotely - put your location in here to see what is available to you https://www.accaglobal.com/us/en/student/exam-entry-and-administration/enter-an-exam/exam-availability-and-booking.html